If you can run to it I personally would choose the CM18
The cheaper Raider has either the short 233mm or long 357mm barrel
(there is no medium Raider)
The front sight is cast into the outer barrel so if you seek to remove it you will need to saw it off and looks rough
To adjust the hop on Raider & Carbines - the dust cover doesn't drop down after pulling charging handle
(so you need to open the dust cover & hold it whilst trying to adjust the hop unit on the 2 cheaper G&G's)
Yes the Raider (rear wired) has rails which is better than messing around trying to convert a Carbine (front wired)
If you have to get a Raider then maybe consider a shorter one if you play CQB - not that it makes much difference
But more that you could extend the short Raider but not quite so easy to reduce a long Raider
CM18 - more expensive than Raider but dust cover drops down as expected
Barrel is 275mm I think & the sights are very nice and easy to fold or remove if fitting your own on there
(Raider's front sight is fixed on there so you are stuck with it or use risers or hacksaw)
Choice of the Black/Tan or Tan/Black versions - hmmmm would of been nice of them to add a full black & full tan I guess
It is a nicer looking gun imho but all the same it is same stuff as Raider inside
Two things to point out on the CM18 - it comes with a 120rnd mid cap not a 300/450 HiCap so you will need a speed loader
& The front flash hider is not my cuppa tea - it designed for quick screw on suppressor but found cheap ones go on wonky
So you might change that like I have done - but that is just my personal opinion/taste
Normally you have the good old reliable options of Carbine, Raider, FireHawk, CM18 and some others like G16 G26 + others
All are pretty much the same inside - it is really down to your own personal choice of these great polymer receiver guns
(there was some 30th edition G16 & G26 made but those were both front wired guns and still think the CM18 is best looking cheap G&G)
Think CM18 is a very worthy consideration even though it is a bit more than Raider as you be glad of the removable sights I'd say
Best thing is to ask others & maybe try to hold a few guns, if not consider the CM18 over the Raider if you got another £30 or so
Hope this answers your questions