I own both types. A Barrett REC7 (piston) and a Les Baer (DI).
The Barrett was designed as a piston gun and not a DI retro-fitted to be a piston system - I think that's an important point. The rifle was designed and built to be piston operated. The REC7 gas block/piston is self-cleaning, self-regulating and will shoot whatever level ammunition you put in it, if you run a supressor the gas block has a position to regulate the gas for the supressor. The piston system adds 3.8 oz weight to the rifle.
Buy whichever you can afford. You're probably safer buying a DI as you can find one that will work reliably for whatever price point fits your budget. Piston rifles are more expensive and you have to carefully look at them for design, operation, and features.