what's the biggest you can afford??? seriously the most common is a 302, next would be a 351. then you can stroke them to 427+ inches. after that you need to modify the front end, then the skies the limit.
if you go into the tech section they spent about 6 pages arguing that very same question recently. your not gonna get a straight answer either way, for a street car tho it sounded like the W is the way to go but i honestly couldnt tell you. there both good motors in their own right
it doesnt sound like your trying to make SEROIUS power or run a 10 sec 1/4 mile or anything like that. your best bet for the money would probably be a fixed up 302, 4bbl, intake, carb, maybe a 80's 5.0 HO block