Um, I'm not sure what you mean by 'BMX/trail bike'. Also, I'm not sure what you mean by 'huge'. If you want to trail ride, you should ride a trail bike. You should ride a trail bike that fits you.
Whenever you start a project, of the bicycle sort or any other, you have to decide two things at the outset - 1) purpose. What do you want this thing to do? 2) budget. Decide what you want to pay at the beginning.
I don't think there's any significant difference between these two frames, frankly. They are both low-end, mass-produced aluminum frames. I also don't think it makes sense to build one up, because I don't think it's possible to do that economically. It's always more expensive to build a bike than buy one. If you don't care about that, because you 'just want the experience', that's fine and probably a good way to learn things about your bikes. In this case, keep the purpose of the bike in mind, and stick to your budget. Good luck and have fun.
Consider the build kits at jensonusa, or pricepoint to keep costs down, if you haven't already.