i wanns eventually learn both instruments but i was wondering what one is better to learn on.
Well, if you start playing guitar, you'll have to adjust to the larger frets and wider apart strings on a bass.

But if you start on bass, you'll have to adjust to the smaller frets and closer strings on a guitar

Personally, I'd say guitar, it's more versatile in that you can play chords on it and not have them sound crap.

But, the next guy to come into this thread could have an equally valid reason for why they think you should learn bass first.

Also, bear in mind that there are more guitarists around (certainly where I live anyway) than bassists. If you wannabe in a band, you may wanna learn bass to increase your chances.

That's why Duff McKagan picked up a bass, look where it got him
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If you cut down on these costs students won't learn so well, effecting the "quality"...
You probably didn't want to hear this, but which one do YOU want to start with first? Honestly, if you really love the thing you've got you're more likely to play it, and playing it often and consistently is more of a concern than which instrument to start on.

Do you like the screaming lead guitar in your favorite songs? Or do you listen to the bass lines and feel the groove?

I just recently picked up a bass because I thought it'd be a fun change from guitar, and it is, but it is certainly different. Some may say it's 'easier' because it only has 4 strings, or because a lot of songs use it in really simple ways, but I'd have to say it's just as hard to play. You still have to get your fingers in the right place, and in the case of the bass, you need to press down harder to avoid buzz, while at the same time being delicate to avoid buzz...

Basically, choose what you find more interesting. If you're a laid back person and you don't like the spotlight, bass might be better. If you love being the center of attention, maybe guitar is better. But both instruments can adapt to both styles. Pick what seems more fun and you'll be more likely to stick with it and most importantly, enjoy your time playing it. Because if you're not having fun, what's the point?