*sigh*
I always DM, I can count the PCs for (A/O)D&D I made on one hand. As for other games, I usually don't get to play long enough to see if the PC is good or bad, let alone to identify what makes them good or bad. I can make some observations, though.
Anyway, I don't like my PCs to be excessively unique, because I feel that uniqueness and originality are different things. Anyone can whine to the DM until he can play a nonstandard race; but that won't make a boring character into an interesting character.
I never look for party practicality in may characters, ever. It's the DM's job to make adventures that cater to the party, not my job to make characters that can do his adventures.
Now, let's see. A thing that I look to achieve when designing a character is coherence between description/background and stats. If it says that he has big muscles and he used to go swim with his parents, he won't have STR 8 and no Swim skill. The right distribution of stats, feats, skills, and so on is the one that matches the concept, so the trick is coming up with a good concept.
I also like to design his personality so that he has some good reasons to adventure and can get along with most people. I strongly dislike characters that seem to be made to annoy or be annoyed, as well as those who would rather stay home and grow cabbage.
If I feel the campaign is not too serious, I make not too serious characters. I like to make social munchkins, maxing whatever social stats the system uses and seeing what the DM does. I've killed two campaigns due to excessive wealth, so far. Well, neither of them was going anywhere in any case; one was a Star Wars campaign where DM pets were sprouting up like mushrooms and the other was a Cyberpunk 2.0.2.0 game where a PC was a vampire (!).
If the campaign is trying to be serious, OTOH, I make good roleplayable characters. Too many players, when asked to make a character with an interesting background, come up with something weird involving ancient prophecies, mysterious family heirlooms and stuff like that. Not realizing that if everyone in a party of 5 has destiny written all over the forehead, the overall result looks just ridiculous. Nah, I'd rather make someone who isn't the average guy but isn't the saviour of the universe either.
Another thing that I dislike is characters that are absolutely the best at what they do. So six people meet and they all have exactly 18 in their primary stat? Yeah, right. This isn't a matter of powergaming, it's just that making every hero a superhero quickly becomes stale IMO. My characters tend to have the right stats for their class but not inhumanly so.
The last character I prepared is for a Star Wars d20 campaign that I hope some day will begin, who is a sorta wookie mystical warrior. Initially accepted into a wookie order of force-using fighters (kinda like jedi, only more shamanistic and less munchk... erm, efficient) on account of his combat skills, he was kicked out because with his whopping 8 WIS and 10 INT he wasn't good enough. He never really cared too much about it, getting into it mostly because of prestige, but he doesn't really have anything else to do, so he got the first ship out of Kashyyk and there's the campaign is supposed to begin. He's a Force Adept right now, but he's going Soldier from 2nd level on. He's incredibly strong but not the brightest or wisest wookie in the galaxy.
So let's see, this character is interesting but not designed to steal the spotlight. He is powerful, capable of dealing nasty damage in melee and of using a bit of Force as well, but not munchkin. He is kinda weird, with his shamanistic outlook, but not disrupting. He can do a lot of things but he's only really good at one - melee.
