what is best 1/35 scale usmc m1a1 kit?

I think you are asking a trick question there Msgt Greg, USMC, Retired who crewed M48s, M60A1s, and M1A1s.  But here goes....

For Desert Storm, any of the US Army M1A1s will do.  I would still go with a Dragon one. Not the USMC version (kit #3531) though, it is a post-ODS tank.

USMC did not have any of their own operational M1A1s during ODS.  They had one Bn or so of M1A1s that they were fielding at Twenty-Nine Palms at the time.  For ODS, they drew a Bns worth of Army M1A1s from PrePo stocks.  They were standard Army tanks with Army smoke launchers, etc.  Nothing Marine-ized on them.   USMC also had 3 BDE (Tiger BDE), 2AR Div attached to them for support, and a Bns worth of Army M60A3 TTS tanks (as produced by ESCI, and recently reissued by Revell, best M60 kits out there) were also drawn from PrePo stocks.  The majority of USMC tanks was still the good old M60A1 RISE/Passive w/ERA version as produced by Tamiya and Academy.  For a good M60A1 RISE/Passive w/ERA, I would take the Esci (reissued by Italeri) M60A1 and add the ERA and other bits from the Tamiya or Academy kits.

Did I pass the test Msgt? 

Hooaah!! 

and 

Semper Fi!!

The Dragon kits also lack the connector box for the bustle rack APU. You will have to either scrounge one from another kit or scratch it (not hard though). 

Best one in my opinion is the Dragon USMC Baghdad 2003 kit.  Comes with lots of extra gear and accessories too. 

Review from PMMS: http://www.perthmilitarymodelling.com/reviews/vehicles/dragon/dr3533.htm

Tamiya's M1A1/A2 OIF also builds into a USMC M1A1HC (Heavy Common).  It is a little easier to build than the Dragon kit, but doesn't come with as many extras.  It is also lacking the anti-slip coating on flat areas of the upper hull and turret. 

Review from PMMS: http://www.perthmilitarymodelling.com/reviews/vehicles/tamiya/tam35269.htm

Neither of the above kits make a fully accurate USMC M1A1HC though.  USMC M1A1HCs in OIF had a BRE (Bustle Rack Extension), the extra rack on the back of the turret bustle for more storage.   The Dragon one comes with a US Army (3ID) BRE, not a USMC version.   Tamiya's doesn't come with one at all.  The only kit that has the correct USMC BRE is the "new" Academy M1A1 OIF, however the rest of the kit is trash.  You can see the correct BRE in it's review at PMMS as well:  http://www.perthmilitarymodelling.com/reviews/vehicles/academy/acd13202.htm

BRE is on the new "J" sprue: http://www.perthmilitarymodelling.com/reviews/vehicles/academy/acd13202j.htm

Eduard also makes the USMC BRE as a PE item too.

Further, they are all missing the EPLRS antenna mount on the right rear of the turret, a power junction box on the left front of the turret next to the man-hole cover, and a power conduit running along the left side of the blow-off panels between the APU power connection box and existing conduits if using an APU in the turret bustle rack.

Read my article here for more info on M1A1 types. 

http://www.armorama.com/modules.php?op=modload&name=Sections&file=index&req=viewarticle&artid=613

I used a combination of Academy hull and USMC parts, Dragon turret, Dragon interior parts, Academy BRE, Trumpeter drive sprockets and track, Tamiya detail parts, and lots of scratch-building to build my M1A1HC "Angry American".

Correct BRE:

More here.

Here is a side-by-side comparison, by Vodnik, on most M1 models out there as well.  It will give you a look at the basic kits.  It includes the above kits.

http://vodnik2.republika.pl/pages/m1-comparison/m1comp1.htm

Good luck.