why is that archie chooses ronnie over betty everytime?

Well maybe because according to the comics, Betty is an average girl just ike Archie but Veronica is rich. And moreover she is much more fashionable that attracts boys towards her. But Betty is simple girl who wants the thing to be simple. May be thats why Veronica is quite dominating.

Betty is definately sweeter nature wise. But Veronica is rich and richness induced beauty. Archie is vain. And therefore has more attraction for Veronica

I think Archie always runs after Veronica is because Veronica is always elusive. She is so hard to catch and always play hard to catch. I think that is the lure for some guys. They always go after the one who is coy of her feelings and hard to get. On the other hand, Betty is the typical girl-next-door who is always available for Archie. Because of that, Archie seem to take Betty for granted. To add, Veronica is more of the glamorous type and has that elusive charismatic appeal that seem to just draw guys in. Betty is more casual and more tomboyish.