The smarmy answer would be the one you have the most fun playing. Smarmy, but also rings true in most cases.
If you enjoy the combo then you'll not realize it's not as uber as the others. If however your just looking for a FOTM build I'll defer to others.
My personal favorite blaster for soloing would be Eng/Eng though. The knockback is an excellent mitigation tool, not to mention the power of the melee attacks.
Other than that I've heard good things about. Ice/Ice, you method may vary accordingly.
Maestro Mavius - Infinity
Capt. Biohazrd - PCSAR
Talsor Tech - Talsorian Guard
Keep Calm & Chive On!
I tried ice and didnt like it. I figured dual NRG would be good though.
Thanks. 
I had quite a lot of fun with my AR/Dev solo'ing most of the way to level 40.
"I want Johnny Sonata to open his Moon Casino so we can have some damn Wailers on the Moon." - Johnny_Butane
"The vet reward for 1200 months of play is we move the servers into your house." - BackAlleyBrawler
Most fun solo was Archer/Device. */Dev is made for solo play. Its a different feel than any other blaster secondary.
ice and dev good secondarys fo solo becase they give u corner pull control
Fire/Ice. Damage with abit of control with the slows and Ice Patch.
I also like Energy/Electric a lot. /Electric KBs even more than /Energy (at least it seems to for me).
Altoholic - but a Blaster at Heart!
Originally Posted by SpyralPegacyon
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I'm running Sonic / Ice. Good Damage, extra holds / sleeps and lots of slows. Res debuff helps out for faster take down too.
Demonfest - 50 - Demon / Thermal Mastermind
Covered Shadow - 50 - Dark Melee / Shield Scrapper
elec/elec, ice/fire
Fire/nrg or Fire/Ice
I give my vote to Ice/EM. It gives you three things that I find make it work very well
1) It has different "stages". In the beginning, first 10 levels or so, you need as much damage as possible. I know its silly, but the fact of the matter is you need to be able to keep yourself going at a constant rate by killing as many enemies as possible as fast as possible, whose attacks aren't as great as the higher levels which means you can skip defense at least for solo. Ice/EM affords you that by giving you 2 attacks right out of the box, build up and aim early, and good melee attacks.
Then you proceed into your teens where the enemies start getting nasty. This is where Ice's holds start to shine and continue to shine. You will have survivability plus damage, which is what you need really.
After that, its just more balancing of survivability and damage, which Ice/EM gives both.
2) You dont have to worry about not going into melee as much solo since there aren't as many enemies, hence why EM is so good.
3) They are both outstanding ST.
I personally liked Fire/Ice/Fire and Ice/Ice/Fire
what is the best combo for soloing?