Fortune & Glory all the way for me. I remember being excited about The Witcher because I loved the video games (well game I only really liked the first one). They released it for PC around the time they released teh physical board game and I was thoroughly unimpressed with it. Seemed very bland and unimaginative. There's at least lots of fun to be had with Fortune & Glory. I had no fun playing the Witcher.
As far as Fortune and Glory, I'm not particularly fond of playing it competitively. It is frequently too quick and mostly determined by luck. I like the cooperative version quite a bit, but it does seem to have issues with the tipping point of the game being relatively early in play.
I love fortune and glory. Just got the two expansions for it too. I'd only play it in co-op mode with a vile Organization but its a great random story.
I got F&G because i fell in love with A Touch of Evil. It's a great 'story' game. The Witcher is more of a race to go from place to place and collect items/clues/etc. While you are collecting artifacts in F&G, there is a story element in it totally missing from The Witcher. If your ok with Random Events (because there are a lot of them in F&G) then i think you'll have a great time with it. The two expansions just came back into print as well, and FFP is one of the few publishers that I'd say their expansions really add to the game and make it whole.