both are great engines. Very tough. Either way, you'll have to take into consideration that the windsor is about 3" wider, 2" taller and a few pounds heavier than the 302. But, it will make more torque/horsepower than a similarly built 302.
351W is a beast (in a good way) but the 70 came stock With the Cleve. All 3 motors have thier fan clubs of which I belong to the 351W fanclub. I had no problems with te half dozen 302 blocks I ran. If stock is no concern, I think the 302 is a little cheaper and easier to go with a roller because of the availability of the roller blocks.
Do some soul searching and come up with some desired HP numbers and tell us how streetable you want it. Also let us know if you run a stick or whatever else you think would be important.
302 can be very streetable up to about 350HP, the 351 up to about 450HP. Either one can go WAY beyond that if you only want to hang out at the strip.