Model 98 with expansion chamber. Revy Hopper (X board) Stainless Steal Kit. and Stainless Freak.
The first upgrade I would get is a new Barrel. Though the stock does perform well in speed ball, In wooded or backyard ball I would suggest either the Flatline or the Freak, maybe a Teardrop.
The Tippmann is well known for its durability.
Hard to field strip. Gas hog.
In my two years experience, Tippmann is a great gun. Its performance is barely out done by its strength. Though it may take an extra couple of seconds to field strip I think its worth it. Tippmann with expansion chamber cuts down on the Co2 use. I would recommend even getting a regulator. All in all Tippmanns are awesome
My final recommendation on Tippmann 98 Model or custom is (listed in order of importance). First new barrel, second expansion chamber, third either a drop forward or remote, and last nitro