Assuming that they're both in the same condition and in the same
ballpark on price, I'd go with the V8. In 1988, I was looking at the
21 ft. Searay Seville midcabin. It came with a 4.3 Merc also. When I
was ready to buy, they had dropped the Seville and upgraded the 21 ft.
to the 220 SDA that you're talking about. They also upgraded the
price out of my reach at the time. I bought a 21 Bayliner w/230 V8 and
I wouldn't want any less power. (I won't go into why I bought a
Bayliner, but price was the biggest consideration and the boat has
served me well for what I wanted.) I rode on a 21 ft. Seville w/ 4.3
and with 2 people on board, it was OK, but with 4 it tended to bog down.

Hope this helps,
Happy boating, Norm