Best Game Engine/Framework and Language for 2D actor/sprite intensive game

If you're looking for something highly optimized and easy to use, Pygame with Python would be my suggestion. Pygame's Sprite and Group classes are incredibly optimized, and it's sooooooo simple to extend them to your liking as well.

SFML benchmarks show it being capable of handling 2000 rotating sprites at once at an acceptable framerate (http://www.sfml-dev.org/forum/viewtopic.php?t=43). I am very curious what you are making that will have thousands of sprites on the screen at once though. I mean if you filled an entire high-def screen with 32x32 sprites you would only hit 2025 sprites used. If you have larger sprites or a smaller resolution, I would expect to be using only a few hundred sprites on the screen at any one time.

I'm wondering what the best engine/framework/language is for a 2D game with thousands of sprites/actors on screen at a time.

The one you know the best.