Differences in Megasquirt versions???

What is the difference between Megasquirt 1, 2, 3?

And why would I want one over the other? I've searched but cannot find a side by side comparison of all of them.

There's a huge comparison list here:

http://ms3efi.com/feature-xref.html

MS1 - fairly basic system, can run fuel and ignition on many cars though.

MS2 - faster processor, allowing for some better control tricks and more precise injector control. Also has a stepper idle control.

MS3 - can be built for 8 cylinder sequential fuel and coil on plug capability, and a lot of features you'd normally only find on very expensive ECUs. Also in very short supply at the moment.

MicroSquirt - tiny MS2 based setup, not sold as a kit. Designed to be extra rugged and originally intended for bikes, ATVs, etc, but also works pretty well for cars.

DIYPNP - a MicroSquirt Module based build it yourself system that can be set up to plug into many stock EFI harnesses.

is sequential fueling best then?

digdug18 wrote: is sequential fueling best then?

Do you like apples or oranges?

The short answer i guess could be "yes." The long answer is: You'd be extremely hard-pressed to see/feel/notice a difference between sequential and batch.