For PVP? I would avoid pretty much all RP servers. Yes some RP servers are super fun to PVP on, but you can only PVP for as long as your money lasts. Once your out of money, that means your out of guns. Of course some RP servers have jobs that give you weapons, but usually said jobs can't just PVP whenever they want to (in most cases).
My all time favourite PVP server and possibly one of my favourite servers of all time was Train Town. Train Town was a super simple server that worked so well it was stupid. You would spawn into the safezone where you can equip yourself with some weapons. Some of them such as pistols were free right away and you would have to level up (just by playing) to unlock more free weapons. The server also utilized pointshop for unique weapons or player cosmetics. The interesting thing about the server is that it only used this one train yard map forever unless a VIP started a map vote which once passed would switch the map to a different one for 20 minutes or a player could use pointshop to either start a map vote or straight up change the map for 20 minutes. One thing that really gave a sense of progression was the prestige system. Once you reached level 50, you have the option to prestige. Once you prestige, you get a "Prestige Package" which was some points in pointshop, a prestige cosmetic (varies depending on your prestige level), some weapons and a prestige token. The tokens could be used to buy some cool things.
Overall, I miss this server. It was a cool concept while it lasted and if it came back up I would be playing it again.