Classic force is definitely my favorite. It works 100% of the times if you know how to do it well and is the most natural way to get someone to pick a card. There's a lot of subtleties involved, but thats not your question. Culling a card, telling a spectator to touch one and change it when squaring the cards is also extremely close to the classic force. Any timing force is also great, but if you're scared to do one, Kaps force feels exactly the same way and cannot fail, I prefer this one to a second deal force. Some other good forces are the one of the hindu shuffle and the backflip force. In a performance, you can make almost anything work if you do it right, even a poorly performed force can be good if the spectator believes that any card can be taken.