Without digging further and doing more research... I would say the Red 98 for for the asking price of $39,990 would be the best buy.
But as mentioned do a PPI on any or all of them. It would pay off.
There is so much to consider... maintenance... has the TB, WP etc. been replaced recently...
Tim kind of went off on you here, but he can definitely chime in and give you a list of preventative maintenance type issues you may want to check.
I'm kind of thinking you were asking if anybody on the site had any information, or may know about these cars as opposed to having people on prime do the research for you...
Anyway, the 91 with that low miles may be a good deal... especially if the preventive maintenance has been done recently and if you can get them to lower the price another $2k to $3k or so. Tell them it is at the end of it's designed 20 year life span.... BUT if you aren't aware of the snap ring issue, then the 91 could be one of those within the snap ring range. (That doesn't mean it is a deal breaker, but it is worth either having the dealer fix if it is in the range, or having them knock off another $3k or so, so you can fix it if it breaks.)
Color and such is a personal preference... I have a Red 91 (which is in snap ring range... so far so good, no probs... but it also only has 43K not tracked type miles on it.). I like Red, some here on prime say it is the fastest color... at least for getting tickets..
Tim and others like silver... and black sure looks nice all polished up and clean. There are many other awesome color selections to choose from too. You can search Production Numbers on prime and get the break down.
Speaking of that, the newer 98 NSX-T (Targa's) would be much lower production numbers than the 91.
You can also run the VIN's past CarFax and do a basic check there to see if any accidents or strange title moves appear with any of the cars. I ran mine through CarFax before I became more serious in it.
It also depends on your budget... the 91 is a good $10k less, but would have the 5 spd and 3.0, where the other two have the 6 spd and 3.2.
The 91 NSX coupe would be serial number 442 which would be fairly low for the 2,886 91 NA1's with the MT. Of which 704 were Berlina Black/Black, and 474 were Berlina Black/Ivory. (USA anyway)
The 98 NSX-T Kaiser Silver serial number 69. There were 48 Kaiser Silver/Onyx MT NSX-T's imported to the USA. There were a total of 245 NSX's for 98, 225 NSX-T with the MT, 15 with the AT, and 5 coupes with the MT.
The 98 NSX-T, Red serial number 114. There were 29 Formula Red/Black MT NSX-T's Imported to the USA. Ben also shows 24 Formula Red/Tan MT NSX-T's imported to the USA.
Stats from Wiki Prodcution Numbers.
http://www.nsxprime.com/wiki/Production_Numbers
There is also the Decoding NSX VIN site that may help you break down the VIN information if interested
http://www.nsxprime.com/wiki/Decoding_an_NSX_VIN
There is lots to consider, from personal preferences, to price (unless you have deep pockets and don't care about price), to condition, maintained maintenance, etc.
Enjoy the hunt... it is almost as fun as driving... okay, I lie... driving an NSX is much funner than the hunt :smile:
Good luck and keep us posted.
:wink: It may be to customize, personalize, set it up for SC or TC, short gears, suspension - improvements or just to make it perfect - just to maintain it to perfection - that is gonna cost you! The better you do you homework the less it'll hurt - course you may miss out - pay after you buy or pay up front the only 2 ways I know of. Course you can pay up front and still end up doing something extra. 
