avoid both. The games that girl1 is going to put you through will not be worth having girl2... plus you're gonna break up whatever the two of them have and put plenty of friction between their friendship, and then even if you have girl2 she's just gonna cry on your shoulder about girl1 OR not fully trust you since girl1's been talking about you already.

Or you can try and talk 'logic' to girl1 and tell her you like girl2, but fuuuuuuck that won't work unless you're smooth as a newborn's ass. Which is unlikely.

Either way, they're not worth your mental sanity.