Your map suggestions:
airtime --> I suppose, would be most fun PGP
arenaball --> No.
blitz --> Sure
encounter --> meh, not that bad.
grave --> Siege maps are liked more by the newbie scene
italy --> Should be fine
jump --> Should be fine
pball_shreds1 --> No.
pbcup_renoir --> With mostly good players it could be fine. But definitely not a popular map (lag issues)
propaint1 --> Good.
rally21 --> Meh, could be fine.
shazam33 --> Good
shock --> Seems to be loved in pubs
skylit --> I don't know what this is off the top of my head
ub_cliff --> go to syncmaster's cable if you want to play that.
ub_rooftop --> Good.
--- Honestly, thinking about it more, the most fun servers are the one's like Superman used to run. Respawn being around 20 seconds, maps are all simple , not many paths. The reason it's most fun is due to the fact it always had a lot of people and even if it was 1 newbie left, the maps were mostly simple enough that it wasn't a problem and didn't ruin the map.
The basic thing is, you wont get 'better' players in pubs often, so you can't really count them on the activity. You need to base it off the newbies, which draw in the better players. Then, a pugbot should be made again instead of a passworded server.
Thats just my opinion.