Manufacturer is generally more important then the style. Generally all airsoft aeg's work the same so how it looks like outside is up to you. Though the advice in the Airsoft Newbie Buying Guide about styles is good. Generally ak47, m16/m4 or mp5 are good starter gun styles due to the availability of accessories and upgrades.
For the price range you specified you're generally going to be restricted to the low or mid quality guns. For $300 you could get a JG. Yeah JG's are China clones but they're getting quite respectable nowadays. JG's M4 runs about $290. You could get one of the G&G cansoft (clear receiver) M4's for about $340. G&G is the cheapest of the midgrade guns. $400-$450 would get you an ICS which is a higher end midgrade gun. Anything else is going to be out of your specified price range.