The 2 power sets don't really play well together actually.
Devices is excellent for soloing if you aren't in a hurry. It's very safe. The trade off is that its very slow. The traits that make it an excellent solo set also make it a horrid teaming set.
Rad Blast's best powers are mostly short range or PBAoE. It's better powers tend to have long activation times (Electron Haze and Cosmic Burst) so it's more of a team oriented set where you can get survivability buffs.
In my opinion the very best pairing(s) with Rad/ would be /Fire for sheer damage output. You get lots of PBAoEs but you'll need to build for survivability. Soft capping S/L defense is an excellent strategy in this case.
The next best choice may be /Ice. /Ice add quite a bit of survivability without the game halting animation times of /Devices. Rad/Ice would be fairly team friendly.
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Hmm, well, rad/fire could work too. It's just that I got the name "Geiger Contessa" and I needed a secondary 
Just pointing out that Rad/Dev can stack stuns from Cosmic Burst and Taser to Mag-6 mez, which makes most boss fights post lvl 18 a breeze. Plus, if you toebomb, the Irradiate+Neutron Bomb should really help mop up after the initial bang. Lts and bosses survive, but again, you have taser+Cosmic burst to deal with them.
Not a bad combination at all, and you can slot 4 of the very nice PBAoE Obliteration sets (2 in Rad+2 in Dev) for 15% Def to Melee + 20% rech + 12% Dmg buff + 36% acc.
I'd look at guides, but there isn't a single Rad/ blaster guide out there. I've looked at Rad/ Corruptor guides, but a) a Corruptor is not a Blaster and b) There weren't any Rad/Traps Corruptor guides which I'd imagine to be the closest I'd come anyway. I did take a look at the Fire/Devices Blaster guide, but Rad/ is clearly not Fire/ so I'm still not sure what to think of doing, what goes together, etc. Also, the two powersets are completely unfamiliar to me in every way, never played Rad Blast, Devices, or even Traps on anything, ever, so I really have no idea what would be a good idea to take/not take/slot with what/etc.
So yeah, what should I be thinking with my power picks and slotting for those sets?