My kin/rad defender is level 40 at the moment so...
You should definatly get: transfusion, siphon power, siphon speed, speed boost, transference and fulcrum shift. The only kinetic power I don't have is repel.
For radiation blast: irradiate, aim, cosmic burst and atomic blast. The only rad power I'm disappointed about is electron haze. Oh and the snipe is really really cool.
I still took a travel power, bit later than normal but I had a different reason for getting it. I wanted acrobatics for the hold and knockback resistance. Combining superjump with inertial reduction with siphon power gives you a high speed horizontal and vertical power.
You can always take stamina in the beginning and respec out of it once you get transference. I took it, but it is doable in lower levels without.
I'll be glad to answer any more specific questions. Oh and you'll love the 'aim fulcrum shift atomic blast' combination 
G-Force
Great thanks, it's my first Defender so I want to try and get it right first time I think I'll try without the travel power and see how I go on.
Thanks G-Force
As a Kinetics / Electrics I'm ignoring Inertial Reduction & going for Air Superiority (which I picked up at 18) and Fly. I may pick up hover at level 24 or so for the knockback protection. At the moment I'm going for more of a sapper character though so it mightn't suit Rad as much.
Fly I picked to avoid mobs in Talos / IP as the lack of +stealth in Siphon Speed can be annoying. I've picked up Haste too: Siphon Speed and Hastes boost each others recovery rates so you can really go nuts.
I'm currently ignoring the need for Stamina too and it's doable. Soloing is where you miss the endurance since in a team you can keep your teamies Speed Boosted and hence in Stamina and they can get on with it while you conserve power. Also you can bum CABs off them, pointing out that they don't need them with you around.
Make a sign : "Will Speed Boost for CABS"
Siphon Speed is lovely, but I can see it being a pain when in the wrong end of a hazard zone.
I originally went for Stamina but this was pre I6 and so powers were more expensive, I would see how it goes, I certainly needed it before Transference.
Post Transference you don't need stamina, I'm sure it would help but I run Acrobatics, Assault and Tactics without any problems with endurance post Transference.
If I was levelling up again, I would go travel powerless and take Siphon Speed and Inertial Reduction. Inertial Reduction is as good as Super Jump IMO.
Also consider getting Hasten as with Siphon Speed and Hasten you can get some seroiusly wonderful Recharge self-buffs and peram Hasten.
I went for the Jumping pool for Knockback/hold and Immobolise protection too. Originally I went for flight pool for this but Hover was way too slow and fly was too expensive to run without stamina.
IMO the optional powers in the Kinetic line are Inertial Reduction ( good as a travel power substitute ), Increase Density ( -status effects + Res to smash/Energy for 60 seconds ) and Repel ( never had it ).
@Unthing ... Mostly on Union.
I'd say increase density is a must its my teams status protections its also going to be stackable and to me its seems the duration of id is a bit longer. Its a great power i'd definately take it.
Personally i dont think siphon speed can cut it on its own its okay but i prefer superspeed and hasten, hasten is a great power and a must to get get transfusion up as often as possible. from 1-50 i used ss and inert reduction and i thought that was great, i don't really use siphon speed in PvE hasten is a much better option.
Oh and don't get repel it seriously sucks.
[ QUOTE ]
Oh and don't get repel it seriously sucks.
[/ QUOTE ]It's a good power, it's just in a set full of must-to-have powers and the one you can drop most easily...
But then again you never saw the value of whirlwind either 
Nope its fun, but [censored]..seriously in large mobs in PvE it sucks just the way whirlwind does.
In PvP whirlwind rocks, becuase of the no rooted animation, however repel still sucks in PvP
I've just created a Kinetics/Radiation Defender who is currently at level 3.
Which powers would you recommend definatly getting and which ones I can leave out. ALSO do I need a travel power if I have Siphon Speed? AND would you recommend getting Stamina, or can I go without that too?