I agree with Hrathen and Dvang- there's no must-haves. There are pilots that are easier/ more obvious in their application or whatever, but none of them are like unbalanced for the points except possibly Vader.
There's really only one pilot I don't think anyone can fnd a use for currently and that's Marek Steele. Other than that, everyone is viable in their own way.
Coming from a game like Warhammer 40k, I find it quite refreshing to not feel I'm practically forced into taking a particular character to even have a fighting chance at putting up a good fight for my opponent.
Now, all that said, the named pilots do definitely have an advantage over the generic dudes. Don't mistake what people are saying here, or at least what I'm saying, I don't want to speak for anyone else. The named pilots and their special abilties outweigh virtually any upgrade available to a generic pilot. If you take a 4 X-Wing list with generic pilots and play somebody of similar skill who also plays a 4 X-Wing list with a mix of named pilots and generic pilots, it's unlikely you'll win. Wedge's ability, Luke's ability, Howlrunner's, Vader's, Dark Curse's, etc., etc. make them much better than a generic pilot because the upgrades available to those generic dudes do not match what a named pilot brings to the table.
You need to use named pilots in your lists, there's not just one particular pilot that's auto-win.
Not to sound like I'm flat out pimping it, but I'm going to be posting articles about the Wave 1 Rebel and Imperial pilots on my blog all next week. Stop by and check it out if you feel like it. I'm posting about Elite Pilot Talents and Secondary Weapon Systems right now.