Which RAM would be better?

Go for a single stick 8 gig ram, it'll make it easier when you want to add more ram later

8 GB ram is the norm now, its soon gonna change to 12 GB

Doesnt matter which company, or even the speed, just get something that looks nice with your system

2400 MHz ram is overkill, get 1600 or 1866, that's more than enough
 
to be honest, with that cpu, its never going to be any good for gaming whatever ram you chose. Best to stick to a budget 2x4 8gb kit and save the rest for a decent gpu and cpu. What ram do you currently have? if i were you, if you have at least 4gb, then i'd go for a gpu upgrade first, ram later.
 


OP says he will be upgrading soon, so its wiser to give him a single stick 8 gig ram and room for expansion than to fill up all his slots with 4 gig ram and force him to discard the old ram when he decides to get more
 


i dont think so, there is no guarantee that an unmatched pair will run reliably, and 8gb is still enough for all current games. So makes sense to get a matched 8gb pair to run in dual channel mode, which will give him the most possible benefit. Would probably stick to 1866 or 2133 as the better value choices.