If you want to team go with Thugs, dark works great in teams, if you want to Solo go with the Stalker since they're better suited for it and fun too.
Easy!
Both, the MM and the Stalker, are perfectly suited for solo-play, but I think the MM would bring more to the table in teams and will probably level faster while the Stalker offers the advantage of ninjaness.
However, both are a lot of fun to play, so... I would suggest playing both. Altitis FTW! 
If it has eyes, you can blind it, if it has blood, you can make it bleed, if it has a mouth, you can make it scream.
ok the stalker is a great at for pvp altho everybody on heros always complanes aboutt hem being over powers and if you work it well you can become an essential part of any team very easily
Thugs/dark mm im at lvl 42 on that combo myself at the moment and your right it is scary fast to lvl the pwoer at later lvls when you get powers like gang war is great. it is also a great combo for the rsf as well alot of pets for fire power and the dark debuffs are almost essential for that
thats my tke on the pros and conz of both builds you got a hard choice there but i would do the mm first then the stalker, as it can be very easy to get bored with a mm about the late 30s so haveing the stalker as well there to swop to when you do get bored
There isnt a problem on earth that cant be solved with the proper aplication of hi explosive's
Darklords of the Underworld/Lords of Light forums [url="http://www.armleg.com/dlotu"]www.armleg.com/dlotu[/url]
Scotlands Bru ill/emp troller lvl 50
Monster Bru SS/stone brute lvl 50
Carman thugs/dark mm lvl 50
I have both a thugs/dark MM and an MA/SR stalker and I can honestly say that the MM matures a lot faster and is, in my opinion, a lot more fun to play. The sheer amount of damage that you can lay down is great along with the security that Dark Miasma provides in terms of debuffs, heals, fear etc is just amazing. I live in fear of seeing the combo nerfed for how fast it can rack up XP once it gets going. 
The stalker is also fun but matures a lot later once you have your key abilities in place. Being able to take people out stealthily is fun but I find it's hard to find a role in teams. If you're not sure whether you're going to team or solo a lot, I'd say go MM as it can do both very well. Either that or do as others have suggested and try both and see which you prefer.
@Dante EU - Union Roleplayer and Altisis Victim
The Militia: Union RP Supergroup - www.themilitia.org.uk
cool I'll think I'll take scotlands advice and see how high I can get Ghost detective, who knows.. at this rate I might accidently overlevel Frank! okay thx for the advice guys!
Once you get your Enforcers, try teaming with other Thugs MMs when you can for those stacking Leadership powers. You'll see. Great stuff!
CoX 50s: <ill/rad> <ice/ice> <fire/kin> <grav/sonic> <ice/storm> <earth/kin> <kin/elec> <cold/psy> <thugs/dark> <fire/dark> <dark/elec> <night widow> <EM/ninj> <mind/icy>
I have a lvl 19 Thugs/FF, if you wanna duo anytime let me know, depending on times etc...Ninth Fathom is his name.
Main 50 & Badger Nine Claws Claws/Regen/Body
Other 50's Ph10x Brute Unjust Law Tanker Samantha Urai Scrapper Codename 1250 Scrapper
Cepheus Defender Nilus Scrapper Electro Field Blaster S.PONGE Tanker
Ookay I'm in a real pickle I'm giving my main hero Firefighter Frank a break and figured I might have a go on villains (Firefightin's a full time job! You gotta have a break at somepoint!
) sooo now I'm having trouble deciding between a Ninja Blade/Ninjitsu stalker or a Thugs/Dark Mastermind both which I enjoy mastermind I find quickest to level but Stalker is just way too much fun and its different from what I'm used too as well! sooo any one can give me any recommandations on both AT's please? 