Should I get a water pump or an air pump?
That depends on why you want a penis pump. TL;DR if you just want to get hard fast, an air pump is fine.
If you're looking to get bigger frequently and don't mind running a bath every time you want to pump, a water pump has the advantage of water being an incompressible liquid - you get a more even pump and pressure distribution around your penis for a gentler swell and less risk of bending, bruising, and yes, bleeding.
Water pumps are generally more expensive though, so keep that in mind when looking at your budget. If you go with an air pump you'll also want to use lube to help with both comfort and getting a good seal. You might also want a cock ring to keep your gains for longer, so if you don't have those, consider how much they'll cost you too.
