8-track cassettes
As noted, the 238 records 8 tracks on a cassette simultaneously. I believe the 688 does also. The 488 (and 488mk2) only record 4 at once. I don't know what the similar Yamaha unit does.
As far is the original question, if you want an 8-track cassette deck, and price is not an issue:
- The 238 is probably the most robust. Once you buy it and a mixer, it will probably wind up the most expensive.
- The 688 has a ton of features, most relating to the mixer. It's sort of complicated to work, though.
- The 488mk2 is simple, and pretty much anyone who's ever used any portastudio can wring out 95% of what's it's capable of without a manual. This is a positive and a negative.
- I don't really know anything about the Yamaha machine, though I believe its tape format is compatible.