Which do you want, the short answer or the long answer...
The Short Answer
I don't care, I do whatever teh song wants
The Long Answer
I can't choose, because to me it's sort of like, you can't have one without the other, and they do intertwine to where one can be the other and vice versa.
The best sounding bands to me don't necessarily have 2 "lead guitarists", but rather, have one or two people rather well adept at doing both, just one does more. Sometimes you have a band like The Cars, I've heard Ocasek do little bit's of lead/textures here and there, and I've heard EE lay down some mean rhythms, but EE is the dominant lead in the band guitar-wise.
Another scenario, the total opposite, you have Iron Maiden, both guys can play lead well, both can play rhythm well, both are very good at doing the same things, but with a different personality.
Or STYX, you have JY, who's more of a flat out rock guy, and usually plays a Fender (style) guitar, while Tommy Shaw is more the fingerpicker and laid back bluesy guy. Both guys have their own style, they trade off, and one compliments the other. You know when it's JY or Tommy Shaw playing lead.
Then out have bands with one guitarist who does everything, like Van-Halen or ZZ Top. Some of those guys can carry rhythm and lead at the same time like a lot of Jazz musicians do, other's just do one and then the other.
In my own bands, I just consider myself a guitarist, my whole point of being there is to play a guitar, period, not be a "lead guitarist" blasting solos everywhere for no intent or purpose, but I'm also not to be a boring "rhythm guitarist" who just strums empty chords for every song. In one of my bands, we have songs with no solos, where I'm just playing chords, others where I'm doing reggae like rhythm things, and others where I flat out shred. Versatility is a good thing.
