I like both picture and written description, sometimes the pic's just about where you want it and sometimes you can't find anything at all close. I do tend to use pictures for myself even when I'm only offering text to everyone else though, just as a sort of character/facial reference for the roleplay in general, as I like to use expressions to shape the character's personality. I'm also more used to boardwide roleplays that usually ask for character faceclaims. Beyond that, I might say looks like (insert picture here) but with (insert changes here), or just give a paragraph or three description. I usually start with the quick, first things someone might notice, like skin colour, height, weight, facial features than distinguishing features and clothing choice. So, it can be a lot easier for the person reading the profile if I use a picture... :/ I prefer artistic or real life pictures when I'm using one, but it really depends on the rp, andif the picture fits.

As for sites I use, deviantart is pretty good, but I've also used [url=http://www.hollow-art.com/searchsite]HollowArt[/url] for real life pictures since you can search for particular features, the pictures aren't always great, but you can find names and then google them. Or [url=http://drakonis.org/]Drakonis avatars[/url] for more fantastical characters. And sometimes, [url=http://www.peterfiner.com/current-stock/]this one[/url] is really good for fantasy accessories.