Depends what you want to do. If you have the full sourcecode of any of
them then you can compile it for one of the others. The exceptions are
deep levels of SYSTEM and bit twiddling where each had its own way.
Topspeed by default S/InOut/IO/ and S/Read/Rd/, S/Write/Wr/
Capable of inline assembler or DIY ASM modules.
Allowed some structured array constants.
Logitech was pretty close to PIM3. Inline ASM as hex constants!
Hardest one to port to unless PIM3 adherence was very good.
XDS M2 was PIM/ISO with some extensions to compile TopSpeed code.
ISTR you had to download separate ancillary libraries.
SB was I think like Logitech but maybe allowed some extensions where
array constants were concerned. ISTR Came with an M2 Chess program which
played rather badly. I ported it to TS and XDS a long while back.
The only one I still use occasionally now is XDS. I mislaid TS.EXE
somewhere along various changes of computer and international moves.
From recollections of a long time ago so subject to memory errors.