Bots/FF Good luck staying awake.
Captain Den'Rath 53* Merk/Traps MM, Rivona 50Energy Blast/Time Cor,Victoria Von Heilwig 53* Dual Pistols/Traps Cor, Crab Spider Webguard 53* SOA, Accela 53* Bot/FF MM,Valkyrie's Executor 53* Broadsword/Shield Def Scrap. On FREEDOM! @Knight Of Bronze
"Hypocrisy, the human inherent." "Let not this work be wasted, apply yourself always."
Bots/FF is indeed probably the toughest. Once you get two Protector Bots all the other robots will be double bubbled by them, plus your bubble. I don't think you need to slot to get them past the soft cap (though you should anyway).
Bots/FF can be made more challenging by raising the difficulty of missions solo or picking fast moving teams (bots ain't fast). This makes survival more of a challenge. However if you want lazy just solo on +0/x4 or something and they'll practically power level you.
Big fan of Thugs/Traps myself. Double up on both the +pet resist and +pet defense IOs (use Gang War as mule if needed). Slot the Enforcer with some +Defense. Add Maneuvers and Force Field Generator on top, you got softcapped pets. Pick up Aid Others and toss out the occasional heal as needed. As for the MM itself, grab Combat Jumping and pick up Scorpion Shield from the Mace Mastery pool. You'll be softcapped against smashing/lethal and maybe even energy, the 3 most common damage types. This is not even including all of the fun debuffing your traps will do.
Thanks for the advice people! 
I am interested in trying a mastermind again. I really dislike resummoning and reequipping henchmen, though. What powersets can I take to minimimze this? How's thugs/pain? Ninja/pain?
I have a thugs/FF but still I still have frequent henchmen deaths at level 40. I'm a lazy mastermind without too much strategy and micromanagement, too. I guess I just want to play the game like I'm watching a movie - without too much effort.
Thanks for any suggestions!