I agree with those here who have said that they don't really find any Pokemon totally useless. There are definitely some that I wouldn't use in battles with friends, maybe, but with the right strategy almost any Pokemon can be dangerous!
I also don't stick with a set team -- I flip Pokemon in and out to suit me, which means I progress veeeerrrrryyyy slowly through games because I usually train up most of my Pokemon evenly. A bit obsessive, but it's always fun to do an E4 run with totally random, unexpected Pokemon. I get bored using the standard powerhouses all the time, especially on second or third play through.
I dislike Bug/Grass types more than any other, though -- idk if I'm just not good at strategizing with them or what, but they always are more difficult for me to use than other types.