in my opinion:

1. SWAT - sounds great, but we can't use it.
2. SWATC - too long
3. SWATX - too long
4. SEWAT - sounds not very good
5. SWTX - sounds great, but what about this link? https://en.wikipedia.org/wiki/SWTX .
6. SWAAT - sounds not very good
7. ASWAT - sounds not very good
8. ASWTC - sounds not very good
9. SWATT - may be, but double T makes people think that it is TOKEN, not COIN
10. SSWAT - sounds not very good
11. 'SW - taken' - too long
12. SWET  - I think, that this link make it impossible like SWAT : http://www.swet.org
13. ST - too short. People won't understand what it is.
14. SEWTEC - sounds not very good
15. STEC - very different from our first idea: 'swat'
16. SET - very different from our first idea: 'swat'

So my suggestion is: SWCX - It sounds and looks great and the only link is this: http://www.swcx.org which is not very popular!