Most Helpful Guy
Tricky. You are young, so a lot of the friends you have now won't be around when you are in your mid-20s, so on one hand you shouldn't worry too much about risking the friendship for the chance at moving that to a new level. On the other hand, late teens can be a stressful, stressful time, so good friends can be worth their weight in gold for those few years... so that kind of makes you want to hold off on potentially blowing up a solid friendship.
On the third hand (it's the internet, no reason to limit myself to two hands...)... if the guy that you are good friends with actually kind of likes you, he could get jealous if you date the new guy, especially if things go really well. In which case you could end up losing the friendship anyway, even if you don't date him.
Add to that the fact that it can be really, really hard for guys and girls to remain platonic friends over time, once both of them are sexually active, and it is starting to look like the risk to the friendship of guy 1 may be a worthwhile risk long term.
So... I would lean towards the first guy. If it works, it will be awesome because you've been friends for so long. So there will be a comfort there. If it doesn't... well, there are a lot of chances that the friendship would have been screwed anyway, over time.