Occasionally I get a new player in my group - either a returning fellow gamer or an entirely new one.
Just about the first question I hear from them, before they make up a guy, is "What does the group need?"
My response is the same - what do you want to play? What kind of guy sounds fun, given the context* of the campaign?
This is how my current group ended up the way it is. Two scouts. Two barbarians (one PC, one NPC), both built as front-line combatants. Two knights, also built as front-liners. A martial artist built to fight. A wizard with an interesting combination of spells.
Where is the cleric? The standard answer is "blub, blub, blub." Swimming with the subterranean sharks. He died, and the player moved on to a new guy he wanted to run. The party probably "needed" a cleric, but they didn't get one.
I know one scout's player has a holy warrior as his backup PC, in case he needs to whip one out on short notice. The knight has a necromancer he keeps tweaking and re-tweaking, and keeps hoping enough folks will show up with a new-fragile-wizard-friendly combo so he can try him out.
It's possible with a TPK we might end up with an entirely different group - no scouts, no "standard" wizard, no knights, no barbarians, no whatever.
But I don't care, and I strongly discourage caring about that.
Even in my DF game, where it's a pre-designed environment, trying to build out a group to take it on is a losing proposition. It might "work" in that you're an efficient, optimized set of problem solvers for the kind of problems the dungeon environment poses. But if you're running a character you'd rather not be running, or your third choice because the group needed a cleric and they already plenty of fighters and didn't need a second thief, is that good? Is "success" in play the cornerstone of fun, or is "this guy does the cool stuff I want to do in my leisure time?" the cornerstone of fun?
So my response is generally the same - I tell people to pick something that'll be fun to run, and run that. The group efficiencies will work themselves out. The lack of a whatever or a preponderance of too many whatevers will work itself out. The fun will just be different than expected.
For this reason I tend to look at PCs in isolation, not in a party composition context. If you aren't totally redundant, and as long as you've got something fun to do, and you'll enjoy doing it, the game will work itself out. This is especially true in my pickup-game format, where the party might have a cleric one session or not, or really need a bunch of fighters but be nothing but second-rankers, or desperately need ranged fire but lack the folks to provide it. Planning around "need" assumes a steady need, but planning around "I'll have fun with one of those" doesn't assume much of anything.
So that's why - if you play with me, pick something you'll enjoy running** and run it. Group needs will work themselves out.
* So for my DF game, the context is "guys who'd go into tunnels full of monsters looking for treasure." In my last game, it was "guys who'd buy into the idea of saving the world from an evil wizard." For one short-lived game, it was "Victorian adventurers who'd investigate strange magics and conspiracies." Given that context, what sounds like a fun character?
** And know how to run. Yes, understanding the GURPS Magic rules is a prereq for running a wizard. Sorry, but there it is, they're simple enough but you need to get them before you play them or I end up explaining them instead of GMing.