I've run just about every tank available, and am happy to say I now have the Ty Davis/IMS tank that uses the KX250 shrouds. You have to buy the pipe and tank as a kit, but you get several attributes:
1. the bike is narrower by about 2 inches. Doen't feel like your riding a bull anymore.
2. The tank holds 4.2 gallons, which is great for those really long trail rides. Saved my bacon just last weekend on a long desert ride. I had less than 1/4 tank when we arrived back at the van.
3. The tank is 1 inch shorter than the other IMS tank that uses the stock pipe. This gets the weight of the gas lower in the frame so the bike does not feel so top heavy.
4. Add a 1993 KX250 rear fender, and the bike looks more modern. (While some folks like the look of the stock rear fender and shrouds, I prefer the sleaker look of the KX250 plastic)
5. The new pipe is stronger than anything on the market, period.
6. Because the pipe mounting spots are different with the new pipe, you don't have to rebuild the mount under the tank.
7. Plug access is great.
8. I think it just looks cool.
I believe the current options are the old style IMS tank, the Clark tank, and the Ty Davis tank. Not sure which one is cheaper, but the Ty Davis tank is definitely the most expensive. IMO, worth the money.
Rick