Holley 1920 VS Carter BBS
The BBS is the better-designed carb, but at this late date the one to pick is the one that's available in better condition. Top № 1 choice would be a new Carter BBS. They do go by on eBay from time to time, and for hookup compatibility you'd want a '70-up (California) or '71-up (50-state/Canada) carb. Expect to pay money; nothing runs like a new carb, and every time someone buys and installs one there's one less in the world. Like
this one. Second preference would be a very carefully picked rebuilt unit like maybe
this, bought from the people who rebuilt it and stand behind it (at least they say they do), a whole hell of a lot preferable to the "remanufactured" garbage one can piss money away on from real or virtual parts stores.
Everything hooks up directly, except the fuel inlet's on the front of the BBS rather than on the side like the 1920. Good excuse to do the
Fuel line mod. If your choke is anything other than perfect, put on a № 1231
electric choke kit when you do the carb swap.