pl_frontier is always fun ctf_biomass is the only CTF map I've played in TF2 that doesn't constantly result in stalemates pl_cashworks is very popular, though I'm not much of a fan The CGTalk server has a few fun customs, though they're often pretty weird. May want to check the maplist out.
"Does it matter if I draw digitally or it's better with pencil and paper?" IMHO you'll progress about 10x faster with paper, as digital is nowehere near as accurate and responsive. And you can always have a tiny dollar store sketchbook/notebook on you, as opposed to having to carry an absurdly expensive and fragile digital…
Vegas is quite fun in Coop I must admit. I'm more a fan of the older Red Storm games like the original and it's expansions. Later games went a lot more, lets say...easy. Siege does look fun, though don't know how long the destruction stuff will hold up for.