Well me and my fellow guitarist write some pretty kool metal riffs, solos, choruses etc......but when we're working on a song, we cant seem to make up our mind on what riff to stick with. we write alot of similar riffs and i just want to stick with one good one you know? and he seems to want to use them all but that would be boring if a song had a bunch of similar rhythms through out

he doesnt seem to get it when i tell him though so idk what to do!!! i dont want to have a boring band!!
If they're all very similar, start with a simpler one, and have it progress and get more complicted into the main parts of the song. That way you'll be using riffs you both wrote, and it won't be as boing, because the riff has a similar feel to it, but is always changing.