This article is from the Amiga CD32 FAQ, by Stuart Tomlinson with numerous contributions by others.
A: The Archos drive uses the PCMCIA slot, emulates Akiko through software (but as far as I know only Wing Commander uses it and that crashes, hmm...), needs you to install the CD-ROM file system to your Workbench before you can use the drive, needs a utility (supplied) to boot CD32 CDs, and doesn't have FMV capability.
The CD1200 isn't available yet. It uses the A1200's trapdoor slot, has Akiko, has Kickstart 3.1, boots straight from CD-ROM, and doesn't have FMV capability.
Peter Kittel wrote: The CD1200 is a prototype CD-ROM drive for the A1200, which makes the A1200 CD32-compatible. This is still in prototype, was shown on a few fairs, and as of now it's uncertain whether it ever will get produced. With it you get CD32 software compatibility, but no hardware compatibility. Especially there is no chance to add the FMV cartridge to it.
The CD4000 isn't available yet. It's a card that fits into one of the A4000's Zorro 3 slots and a CD drive that slides into a drive bay, has Akiko, has Kickstart 3.1, boots straight from CD-ROM, and has FMV capability.
The Squirrel uses the PCMICA slot, doesn't appear to emulate Akiko, needs you to install the CD-ROM file system to your Workbench before you can use the drive, needs a utility (supplied) to boot CD32 CDs, and doesn't have FMV capability. It's also a full SCSI interface. If you'd like to add other SCSI devices (such as tape storage, scanners, etc...) then it could be a better choice than the Archos. Also software updates are regularly uploaded to Aminet (unlike Archos' where you have to try to convince your dealer to give you a free copy).