Of course the TRUE least favorite would be some trash that never should have been pushed out, but if we're sticking with well known classics, I'm going with Castlevania 1-3.

The controls on those games were terrible. You were slow and clunky. Jumping between platforms required a trigonometric calculation. The weapons had a very specific and often a very strange path that

Enemies dipped in and out of attack range, and it constantly felt like I was supposed to press the attack button two seconds before the enemy was even on the screen.

I'm sure its not so bad once you memorize the levels and get used to the timing, but I have enough good games in my collection, that I don't need to waste my time adapting to the flaws of these games.