Whatever a player ends up buying, they will get used to using and maintaining, I don't think that is really ever an issue. What's an issue is how much you want to spend initially in proportion to how much it can be used, effectively.
based on a buying new budget, going GBBR will be the more expensive route, from a firefight effectiveness point of view, AEG would be a safer bet, unless everyone you know plays with gbb, then it's an even playing field.
When you aren't constrained by budget limitations.. ie, saving up for a while, lots of disposable income. (single, well employed etc :P) you can do whatever you want really.
But most people tend to make recommendations on the cheap to start... why invest 1000 into a rifle and mags to find out in a year you don't like it or don't have time for it... you turn into one of those guys trying to sell their 'LNIB gun for 50 bucks off of retail after you've gamed it a couple times'
An AEG with 1 highcap can be fielded in a skirmish, much to the chagrin of the highcap nazis, but it's ready to play, if the person likes playing they can buy more low or midcaps.
A GBBR with 1 realcap mag will need several more mags to make you even remotely effective in a firefight. So you pay as much if not more as an AEG for the rifle and then that again that for mags.