So much depends upon your preferences.
I have an S-Tec 30, which (along with its cousins, the 20, 40 and 50) is a rate-based autopilot which can operate entirely autonomously, save and except it requires electricity. Hence, it is a nice back-up to your attitude indicator.
The S-Tec 60-2 and 55X are also rate-based, but require a heading / course deviation input to operate.
Rate-based units are great, but they are less stable in really rough air.
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The Century units are attitude-based; I have flown behind the Century 2000, and it is (if properly dialed-in) amazingly good, flew a coupled ILS like it was channeling Ernie Gann.
Note also, that Avidyne is working on getting their DFC90 certificated in various airframes - may be a while, though.
Spending my own money, today, I'd probably still buy an S-Tec... but its close.
Tell us more about your requirements.