TNA will struggle to secure MSG, since it's heavily dominated by Vince.
I'd like to see them in the New York market for B4G, and run the Hammerstein. Cram as many fans in there as possible and provide a real epic atmosphere to the show.
As for Slammiversary, I'd nominate Nashville, going back to their roots and all. Would make the spectacle of the 'anniversary' feel a little more significant.
Nashville sucked for TNA the last time they went there so I'd rather not....
Isn't Hammerstein's capacity for wrestling around 3,000? I'd think TNA could get more out of the show in New York.