I think Thanos has a very good chance of wining this, but I also see the Annihilators slowly picking him apart.
Gladiator and Beta Ray Bill should certainly possess enough strength to subdue Thanos, while the Surfer, Ronan, Quasar, and Ikon could quadruple power blast him, not to mention Gladiators laser vision.
This one is hard to judge, but I give the slight win to Thanos after a long exhausting battle.