This is what their datasheet says..
R-305 claims to take less search time than SM-630 (But I believe it won't matter). Consumes a little more power than the other. And can store less templates than SM-630. So it all depends on price, availability and your choice.
I would recommend SM-630, because it can store 768 templates and gives the possibility for more future enrollments. But for the project, you might not need so much memory. So here cost plays its part.
I have a same project for my college, but I am not buying any fingerprint scanner. Instead, I am building my own. But take my advice, that's a lot of hassle to go with. :bang: But it will save some bucks...