S thunder tiger 91 2 stroke would give you the best bang for your buck, they have been compared to OS engines and although they have a slightly lower preformance spec, it isn't by much and the reliability is second to none, and as I said you can't beat the price
My TT .91 will outperform my old Surpass .91, perhaps on par with the newer Surpass. The manufacture power specs are meaningless, and OS numbers are very inflated. I don't recommend it for a beginner because of the long break in. Probably even longer than a Saito.
After thinking about this, if you want a cheap two stroke then try the Tower .75, a little more then the Fox .74 its stronger and will last a lot longer both are about the size of a .60. Four stroke, well for a beginner I suggest the OS or Magnum .91. The OS is more user friendly and better built. Saito's and others take longer to break in but last longer. IMO a .91 two stroke is too large for most beginners in this plane.