Which Atari ST emulator is recommended for speedrunning because i'm planning to speedrun a Atari ST port of a game called Tom and Jerry: Hunting high and low not sure if this was a right place to ask though

TBH the more simple systems are more easily emulated. You are probably not going to go wrong as long as it works, but you may want to ask in some Atari ST game forum. What is a popular Atari ST game on speedrun.com? Lol.

I was gonna say ask the mods of the game... but emmm I looked around at some games and only found one rule on one game the only rule was about clock speed. "When using an emulator, set CPU clock speed to 8 MHz. " so I think its up to you and what you think is best for the game :)