Tippmann A5 - The Tippmann A5 is very similar to the 98 custom, but has the cyclone feeder thus it can shoot faster. The internals of both guns are very similar. In my opinion a stock A5 is a little better than the 98 custom, only because of the cyclone feeder.
Tippmann 98 Custom A.C.T. - Response Trigger, Cyclone Feeder, X-7 hopper, J&J 20 inch ceramic barrel, Apex Tip
The stock gun is alright for begginers, but in my opinion the most important upgrade is the response trigger because it gives you so much more fire power.
Many upgrade options. Very reliable. Cheap.
The 98 custom is a very reliable and good marker. There are many upgrades you can add on to it. For only about $140 you get a very good marker. Its also very easy to maintain its good working condition. I consider more of a woodsball marker than speedball, but if you get some fire power upgrades it does great in speedball.
I would for sure buy this gun if you haven't already. It's a great product and Tippmann did a great job on it.