Notes on NeoLemmix and Superlemmini: they are unofficial ports to modern PCs which are mainly designed for playing custom levels. Neolemmix is very widely used by the lemmings fan community, superlemmini has very few users currently. Both have framestepping built into them, with neolemmix having more options in this, allowing users to skip forward any amount of time they want and create savestates. Both have a fast forward mode, and have most glitches removed. Both do not use timers for bombers. They are created to remove the difficulty of execution, and instead focus on puzzles in custom levels. Some minor differences between engines are listed here https://www.lemmingsforums.net/index.php?topic=5343.0

They could be considered different unofficial game in the lemmings series rather than purely a port, or considered an updated port depending on who you ask.

Did some further experimentation and found the in-game clock is also affected by this 10% speed difference, i.e the NTSC game-clock runs 10% slower than PAL along with everything else. So if you want to go for purely in-game time, then the NTSC version will be a bit easier.

I am a TASer, and I have been using the PAL version of lemmings for my MD/genesis TAS. The PAL version of lemmings actually runs 10% faster than NTSC on this console, whilst NTSC has a higher frame rate, the physics of the game updates every 3 frames in the PAL version, and updates every 4 frames in the NTSC version. So it would likely be best to use the PAL version for your runs. The PAL version is also a bit easier to find online (which is the reason I started using it back in 2017)

I wrote a bit more about it on the forum I write about my TAS in https://www.lemmingsforums.net/index.php?topic=2425.msg89912#new