The 2003 TMNT sewer playset is the best sewer playset.

This is not an opinion, this is a fact. Yes, the 2012 one is the largest, but relies on cardboard to reach the height. Not to mention that it is literally a back wall with some dangly bits for play action. It looks busy but has so little.

The Vintage Sewer Playset is cramped and you can't  have the 4 turtles and Splinter in it without it being overcrowded. But it kinda looks like the Turtles actually LIVE there, which if it was bigger, it would be a cool way to display them.
The 2012 set could house the Turtles, April, Casey and Splinter plus a rather large invasion force by the Foot. The problem, as I satated before is that since it's a back wall with dangling bits, you mist have characters hanging in weird ways.

The 2003 playset is a balance between both extremes. It's a little bit on the blander side, like 2012, but it does have a little personality in some areas. It almost looks like the Turtles COULD live there... or they recently moved in and haven't truly decorated yet.

-"But Nefty, what about the Epic Sewer Playset from Rise of the TMNT?"

You HAD to bring out Battletoads... Despite my feelings towards the cartoon, the playset is decent. I can't lie and say that it's a crappy playset, but it combines the worst aspects of 2012 and 1987. Yes, that Playset is huge! The problem is that is segmented in so many many sections that it becomes quite cramped and crowded very easily. As much as it pains me to praise something based on that series that playset is the second best Playset for Teenage Mutant Ninja Turtles.

-"Now, wait a minute Nefty... You only mention old stuff,  when you want to campaign for something... What's your angle here?"

Me? An Angle? Do I look like an Olympic medallist to you? I suck... it's true, it's true! You are correct in the notion that I'm campaigning for something to be made...

And it's not the sewer lair. If Super 7 Worth to make 1 Teenage Mutant Ninja Turtles playset it has to be the Technodrome hands down. A sewer lair backdrop can be customized easily: foam boards some thin PVC pipes, and some 1:12 and 1:10 scale items to complete the look.
1:12 is the 6 inch scale of the Figuarts TMNT, or the Mirage TMNT by NECA, 1:10 is the 7 inch scale for the Super7 TMNT, or the Movie TMNT by NECA. If you're going to work on the 1:10 scale, you must remember that the furniture must be in that scale. Food items you could get away with using 1:12 scale, but if you use furniture in this scale it'll be way too small for the larger Super7 and NECA TMNT movie figures.