Yeah I think Blackwater was the most "oooh shiitttt" episode for me (I think it was season 2 episode 9). My favourite though definitely was Oberyn v Mountain. If I didn't know what was about to happen I'd have completely lost my shit. The effects on the face boom and the way it just ends, I was still in complete shock.
Bastards was just way too predictable for me. Jon would be stupid and fail with tactics, have a weaker team, get them all killed, Sansa would turn up and save him with some white knights. The whole point of the first 4 seasons or so was utter disbelief at some of the shit that was happening (neds head, jamies hand, red wedding, joff wedding, but you knew this was what was going to happen 5 episodes before.
Then again, it was the highest budget, most epic, most brutal, best shot, and the protagonist wins which are all positives so I can see why people like it.