Well, apparently you pretty much explained the benefits of both in your thread at GOG. It seems like you've already tested sneak attack based on your post in that thread. And if you really haven't, then it would appear that you at least know how it works, so what exactly do you want to know? I'll give my opinion if that's what you want, but whether either one is useful to any great extent depends on your party and strategy.
Backstab is a 2E feature, which makes it canon for IWD and HoW. Sneak Attack is a 3E feature, but only Icewind Dale II uses the 3E ruleset. Personally I'd just go with backstab because it's actually a 2E feature unlike Sneak Attack.
Yea just really looking for opinions. Since that post I've played through the whole game using sneak attack and it worked surprisingly better than I thought though it requires alot of micromanaging. At any rate, what I meant to say was backstab. But I know how backstab works from playing the Baldur's Gate series. I'm currently playing a new game and I'm going to try out backstab all the way through. Just wanted to get some other peoples opinions, that have used both extensively, and see how they compared in their games. The stealth bug is really odd to me. Sometimes it works, other times it takes forever for it to engage. It will even work right in front of another monster.