If looking at a '70s deck then Nakamichi and Tandberg pretty much ruled the roost. The big Nak 700 was a fabulous deck and still sounds great, even though limited to Type I and Type II tapes. Amazing to think it arrived in 1973!
Overall though quality improved dramatically around '79 with the introduction of Metal tape and a pulling together among manufacturers to try to stick to a more cross-compatible set of standards.
The best performing deck overall from the '70s may well be the Nakamichi 582 or 680 from '79.The 582 was used a lot by tape manufacturers, testers and reviewers as a tape testing tool. Oh, and of course, just about squeaking into '79 was the Nakamichi 1000ZXL...
Outside of the really big guns from Nakamichi, Tandberg, Pioneer etc.., Sony introduced the first truly modern '80s mainstream deck in 1979 with the TC-K75 (nee TC-K81). It had 3 heads (All Ferrite first then quickly replaced by Sendust and Ferrite for better metal performance), dual capstans, and a full sensitivity and bias alignment system for all tape types. It very much set the blueprint in spec and performance for top end decks to come. A good TC-K81 is still a fantastic performing cassette deck today. Brilliant to use too.