What speaker cable for Martin Logan motion series (AMT) tweeter.

Depends.  What cables are you using now, and what specific improvements/sound characteristics are you looking for?  Also, what’s your budget and are you looking new or used, and do you want bi-wire or not?

I dont need to biwire, I am using some cheap Mogami now. I can go up to $1,000 for a pair of speaker cables. I just don't want anything to sound too bright. 

If you bi-wire I’d highly recommend these AZ shotgun cables that are in your price range.  I have them and they’re nicely detailed but not bright at all with great tone and 3D soundstage abilities, and a few people here have replaced Mogami with these and have been very happy.  Best of luck.

https://www.usaudiomart.com/details/650117484-acoustic-zen-satori-shotgun-biwire-speaker-cable-8-foot-pair/

I am using Canare 4S11 speaker cable connected to the GE Triton Refs speakers with AMT  type tweeter.  No harshness, just pure treble. 

@bobrock 

^^^^ Yeah what @soix said above, when you said $1000 budget the first thing that popped into my mind was that is exactly how much Satori’s retail for.

Grab a used double-set for the same price