Sol Torpedos are the fastest in the game with a speed of 7, but also the weakest with a measly damage of 3. Sure, the extra speed is great for hitting more often, but at such a low damage your target will barely notice they've been hit. I'm not sure trading half a beam-length of extra speed per move phase is worth 3 damage. Sol has one crew disk and two techs that increase their torpedo damage, though. You get can up to 8 damage for a reasonable investment of 7 points. That's more like it. But there are only really 3 or 4 ships in the fleet that have enough torpedos on board to merit the investment, so most of the time you're better off loading up with missiles on most of your boats and only beefing the torpedos occasionally on the right vessels, and then mostly for variety's sake.
Sol has some pretty decent squadrons. The nicest thing about them is that fighters and bombers have the same top speed, so it's very easy for them to fly in formation and support each other. No other faction can so easily coordinate their squadrons without somebody wasting their speed potential. Sol's two carriers are decent. Terra Nova isn't so much a carrier as much as it's a combat cruiser that happens to support a few squadrons. The other carrier comes with absolutely no armament whatsoever. The shields of 6 are decent, the hull of 3 not so much. At least it has decent capacity, both for squadrons and for disks. Keep it out of harm's way though as it is defenseless, and no amount of crew or tech will really change that as there's no foundation of offensive capabilities to build on. The best you can hope for it to turn them into a troop carrier for boarding actions, but that's also a lot of eggs in one basket.
Sol Fighters are excellent. They do the same damage as Sol torpedos, but with a 360 degree firing arc, no reloading required. Their hull of two and speed of ten make them fast and resilient in a dogfight. I consider Letnev's fighters to be the best and their only edge over Sol is a slightly higher top speed. You can use them to hunt other squadrons or ships with equal effectiveness.
Sol Bombers are also quite good... too bad their torpedos are terrible. They're fast, and they are the only bomber in the game with a beam characteristic. This means they can fight back somewhat even when their payload is gone, esp. against other bombers or N'orr fighters. Since fighters do just about as well against capital ships as bombers most of the time, you're probably better off loading missiles on the bombers and letting them handle enemy squadrons while your fighters make attack runs. This is a role reversal when you consider the usual jobs assigned to strike craft, but hey, whatever works, right?
Sol is second only to Sardakk N'orr in boarding actions. They have several crew/tech disks that improve teleport penetration, range, and ignore the need to lower shields. While they don't have access to the cheap Brood Bay, most of their ships are high capacity (or can be made so with tech/crew) so it shouldn't be too much of a problem to fit an away team on board. There's also the Merc version of the Assault Pod in any case. I highly recommend using the Saratoga cruiser as a boarding vessel... it has tons of room, good hit points, but unremarkable weapons. Load it up with some marines and some teleport disks and it should be able to take a pounding and survive to deliver its cargo.
Sol will never match Sardakk N'orr's ferocity when it comes to boarding, but they're no amateurs either. On defense, your high-capacity ships are more likely to have security teams around to thwart boarding attempts, or at least delay the interlopers long enough to transport some of your own marines aboard to save the day.
To Beam or Not to Beam... There Is No Question
Almost every Sol ship has an "okay" beam rating, and this can be further boosted with tech and Crew. Notably, the Weapons Officer can increase beam damage by 2 in addition to any tech you have, but the most important thing to note is that Sol has two crew members that increase chances of critical hits. Granted, this is not as good or as cheap as Dala Mandas, but unlike the Letnev First Officer they can be placed on multiple ships. Combine this with one of Sol's two gunships and some good tech or crew that allows multiple shots, and you can do some pretty crippling damage from a good distance away. Remember, any "Instant" abilities you use count for every shot you take as part of one orders phase. Even if you don't kill them outright, most critical hits can seriously cripple their target's ability to do you harm. The only downside to Sol's talent for beam weapons is that they only have a single UNIQUE crew member that can cancel a beam critical hit. Make sure to put this guy on the ships where you've invested most heavily in beam power, just in case you need him to save the day.
Always Room for One More
The Federation of Sol should never feel cramped when it comes to space aboard their vessels. No other faction can come close to them when it comes to expanding ship capacity. Even the Viking and Terra Nova, which come with only 2 capacity apiece, are no obstacle to creating completely decked out vessels. This is due to 3 techs and 2 excellent crew that increase or modify capacity. Not only will this ensure that you can create the perfect combination of disks, but any leftover space can be filled with Security disks which will help discourage opponents from boarding actions.
All that extra room is both a blessing and a curse. While Sol ships are fine, few of them are truly excellent, and NEED extra crew and tech to be really superlative. That means there's always a danger of over-investing in a ship. Certain critical hits could wipe out your carefully-selected lineup of bridge crew or make all that fancy tech worthless. If you're going to load up on valuable upgrades, protect them with Medical crew or Emergency Breakers. The loss of a ship may affect you more than other factions if you have more points invested in each one, and more points invested means fewer ships than your opponent in general.
In addition to plenty of leg room on their ships, Sol may be the best at making those ships respond to developing circumstances on the fly. Their crew has a good selection of every order type, and more "Activate Crew" orders than any other faction so they can execute multiple orders in one go. In addition, they have three separate crew/tech that can be used to refresh previously-used disks so they can be activated again. This makes for incredible flexibility in combat. I often find that by the time the third order phase has come around, a lot has happened and my ships rarely have the ideal order in the queue. With Sol, I'm more likely to be able to make that last order an "activate crew," and actually have some crew left over to provide me with a few options.
Strengths: Capacity, Beams, Flexibility
Weaknesses: Torpedos, Fewer and expensive ships that can be vulnerable to Critical Hits
Fighting the Federation
Try to focus your fire. If you can concentrate your fire and take their most pimped-out ship, they could topple like dominoes. It's probably not a good idea to try to board them unless you're Sardakk N'orr... all the extra capacity will mean plenty of security or worse, self-destruct devices. Their squadrons will be dangerous but their carrier's completely defenseless. You also want to reduce your chances of suffering critical hits... take disks that provide "Critical Hit Resistance" or that cancel the crits that would hurt the most. Sol is unique that they can do almost everything well... so really focus on your own faction's strengths and be better than they are at those one or two things. They'll beat you every time at the "diversify" game.