Sentinel 4’s a bit trickier in this regard – I remember Shunt was very obviously a great Endless map, but in 4 you have to consider the slots available for larger towers, which ones you have upgraded, etc. A few ideas off the top of my head:
– 23 Crystal has limited slots for large towers, but it’s got a sort of spiral layout going on which means enemies will pass towers more than once.
– 20 Cliffhanger has a long path with one entrance, and lots of space for 2x2s at the start of the path.
– 24 Behemoth has a nice big open space in the middle once you’ve cleared out the eggs, but it has two entrances and once the barriers are down the Stronghold is left pretty vulnerable.
– Campaign 2 level 5 is pretty cool if you fill it full of Orions, that’s my go-to “screenshots for publicity” gimmick 🙂
I’d be interested to hear what you discover – if anyone else has suggestions I’d liek to hear them too!
.