There are plenty of excellent, reliable .308 Piston ARs out there. The LWRC REPR is probably the king of piston AR10s, but PWS, HK, and SIG all make excellent rifles. The gus at PWS have run the hell out of their Mk2s and they are extremely robust. Now, personally, the only AR10-style rifle for me is the LMt MWS308, which is DI, but they may introduce a piston kit for it in the future like they did with the MRP, but I'm not worried about the reliability of the DI. The Brits have been using the MWS308 with a few modifications, such as a slower twist for their barrels, for the past few years and it has proven very reliable in combat conditions.
Now, you will pay for these rifles, especially the HK and REPR. Me personally, if I was going to look for a piston AR10-style rifle I'd get either the REPR or PWS Mk2.
The main question is are you looking for a battle rifle or a precision/DMR rifle? If it's a battle rifle a piston would be great, but DI would be fine too. If it's a DMR type rifle you may want to consider a DI rifle. If you're wanting to do both, well then you'll just have to look at the options on each rifle and pick the one that has the most of what you want.