Anyone you want. There isn't much difference between them in real apps anyway.

I'd go for the ITT. The Cyrix one has no rating - it probably can't do 40 MHz. The Green Math on the other hand supports the additional FPU operations of the 487. While this seems good, it can cause trouble with some software, since software either detect a 487 and expect to run on a 486 (which usually freezes the system), or does not expect a 487 on a 386 and will make no use of the additional operations. I have exactly that issue in one of my 286 systems with a 3C87 FPU.

//edit:
Since the Green Math clearly says "DX", it probably won't work with a 386SX anyway.

Do you have any info on GreenMath 487 fpu? Many just renamed 387 to 487 to reflect the 486SLC and DLC upgrades. But performance didn't change.

Nope, those existed as well but were labeled accordingly:

The Green Math chip definitely shouldn't work with a 386SX. Despite being PLCC it is indeed for a 386DX or 486DLC. However, the only 386DX motherboards I have ever seen that can accept the PLCC FPUs without an adapter are made by ALD.

Green Math is an OEM relabeling job. It's either USLI or IIT (I forget which), but the model name seems more consistent with IIT.

The Reveal chips are actually pretty nice, as they are just normal Fasmath chips. It's still inconclusive if they will work well at 40MHz. I once saw an earlier version of the Reveal retail packaging and it said that it worked up to 33MHz, but I would imagine if the datecode is a later one 40MHz should be fine. Cyrix did infact make 83S87 Fasmath chips that ran at 40MHz, but they seem pretty rare.

The IIT chip you have is obviously for 386DX systems, so actually you're only choice is to try the Reveal.

Oh glad you asked this. I have a 386sx-40, I’ve been considering adding a 387 too.