There are many different types of glasses, but in the end it all depends on whether you put Coors Light in it or Heineken.
It's good that you aren't trying to cheap out by buying clone. VSR10 and M24 are both good guns, lots of upgrade parts available as stated. Also said, the VSR is light and plasticky feeling, but can become a tack driver with good upgrades. The M24 is heavy cast metal with a solid composite stock. You can fall backwards with it slung on your back, have the end of the barrel catch in a Y branch of a tree 6" off the ground, it'll stop you without any damage (when I did exactly that, my scope got shifted in the rings a little bit).
One huge benefit of the M24 is the fact it takes AEG barrels and hop up rubbers, and the trigger assembly is good solid steel, adjustable, and stronger than anything, so you use a 600fps spring if you want, the sear won't break (but heavy ass'd trigger pull). The VSR needs upgraded sears above a certain velocity (its low I recall), and i've heard of guys putting them in and running the gun at 400fps and still having the upgraded sears break. Only option then is the 'it's expensive, but it's worth it' Zero Trigger.
And after a bunch of years running my M24 at 500fps w/.20, a few years ago I set it up to 395fps in order to be able to use it at a urban type game (lots of CQB), and loved it, longer range, more consistancy and accuracy with Bastard 0.36g.
So, choose your glass, and fill it with the brand of your choice.
