I wouldn't spend all of your money on just the gun, you might want to get mags for it too. So if you're going that route, get a sportline or ECHO m16/m4 and spend the rest on mags. As for brand It is up to you, I prefer CA, some Prefer TM, some prefer ECHO so on and so forth. If your friends have one or someone you know does, use theirs a few times see how you like it, try different brands and models see how you like em.
If however you want to spend all that money on one gun, then get a full metal AEG for a little more. Same as above use the product before you buy it.
Hope this helps, feel free to ask more Qs
-bryce