I would say either /trap, /poison or /dark. For your pets, Bots i say have best bet, Zombies can do pretty good too (great with dark, double fear).
Most builds for these are pretty straight foward.
50)Sinergy X/(50)Mika.
(50)MaceX/(50)Encore
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Any MM combination can solo from 1 to 50.
/Traps and /FF will be a little easier than the rest due to mez protection, but /Dark is also very powerful.
Poison is generally best in one-on-one encounters, but your survivability will depend on the AV. Positron, for example, tends to laugh at Masterminds and grind them into soggy little lumps. Soloing Elite Bosses (AVs/Heroes on anything less than the highest difficulty setting) is doable for most if not all MM combinations.
For Primary, Thugs are probably the most damaging overall but sacrifice survivability. Bots are by far the most survivable and are great at AoE damage but not so good at Single Target damage. Ninjas are best at ST damage with a bit of control. Mercs are best at control. Necro is a ST Damage/Control/Survivability mix.
Merc/TA looses often from EB's though 
Although the stad-100ft-away-a-keep-summoning-pets tactics seems to work.
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Ok guys and gals ive gone with Thugs/dark but only lvl2 as i only wanted to make it for now due tto currently lvling a corruptor how would this power set do in soloing against EB/Av/Heros??
thugs dark does pretty well against hero and avs.. i have 1 at lvl 50 and had alot of fun gettin there.
Kin Hell Fire
Barline
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Slushy Kins
Nuria Dark
heyy guys and gals is their any builds for a mm that would be able to go from LvL1 to LvL50 without teaming and by that it will need to be able to solo heros and av's without needing help from and other arch all comments welcome except stupid 1's and if you can post a build 2 that would be lovely cheers all