Neither. Get DL or 

The new Progress System is no longer a mystery. Several YTers have put up videos of the new accounts that already have it (this is an A/B test so it could change slightly but I doubt it). I transcribed a list of the items for different tiers in this thread on the WR Forum (a couple posts down) and another forumite created a Google spreadsheet you can access to input your hangar values and see which tiers you have unlocked already:

https://war-robots-forum.freeforums.net/thread/50130/new-progress-path-unveiled-sort

As for your question. Between the two I would get RG16. It is a bit limited but endgame players do still use it. It is most useful in FFA and 2v2. Don't bother with CB12. If you don't yet have DL12 or DL16, you should get those first.

Get the railgun it will do way better damage than the carbine

Carbine needs an upgrade or rework I just get out gunned using carbine 12&10 vs like arc torrent 10&6 it's a joke