Walz does great work, but you may be able to pick up a KP2 on the cheap. They are fun too.
As for Sheridan guns, they are simply the best platform I've ever used in terms of reliability and ease of maintenance. They only have 3 o-rings in the stock configuration.
Yes, you have to have the valve tool, but like many have told me on here, very worth the ~$25.
Most importantly, have fun out there. Nothing more satisfying then watching guys dodge my shots at 30 yards.