UKH

To assist with blowing up the neoair thermarests... should I get thermarest's own sack? or robens? vaude? sea to summit?

anything to choose between them other than volume and weight?

I've got a sea to summit one (which is great) BUT it is designed to work with their valves only. It definitely wouldn't work with the thermarests I have.

Do thermarest even make them to fit their valves? I'm testing an Uberlite currently, and can't see what sort of pump or air sack could attach the valve on it.

I bought the Thermarest one for my Neoair, bit fiddly to put on and keep in place but other than that works fine.

Robens and sea to summit would not work on a thermarest as the valves are different. 

There is mods for making certain models to fit NeoAirs, not sure about the Robens or sea to summit though, here's the Exped one that the OP didn't mention but might be an option:

https://www.gygago.com/index.php?id=724&lang=en

I would go for the Thermarest AirTap Pump (as in just the £10 jobby you punch through any old air-tight bag). I used it on the Appalachian Trail and the plastic bag it came with only broke after about 4 months of using it every night. When that happens, a garden refuse sack will do the job. 

I have the big orange pump sack also but it's quite fiddly to get over the valve and I'm convinced it will break soon at that point. 

The Airtap on the other hand makes the part likely to break (the bag) completely replaceable at pennies. 

It's also a fair bit lighter and a third of the price.