If you aren't prepared for some MIDI programming to make things seamless with this old rack gear (MPX1, G2, PCM/70/80/81, Eclipse, SPX90 and so on), then don't even consider them. You'll have drop outs when you play if you try to switch patches during jamming. There are ways around it by living on an algorithm the entire time and using MIDI or SysEx to turn on/off certain portions of the algo, but it's going to require you doing a deep dive on how the algorithms work. These units sound vastly superior to the ones I will list below, but it's the main tradeoff you're gonna need to deal with.
My recommendations since I didn't see any budget, and I'm assuming you don't want to become an algo expert:
* Rocktron Intellifex/Intelliverb/Intellipitch - Analog dry-thru when HUSH is out, decent overall FX, AnalogKid85 has some cool patches. Around $150 to $300. Add more for the verb/pitch models
* TC Electronic G-Major 2 - Probably the most versatile of them all for the price and form factor. Has basically all the FX you could want, easy to use, can channel switch with a TRS jack, intelligent pitch shift, etc. Around $300. Don't pay too much more than this
* TC Electronic G-Force - Nearly the same as the G-Major 2 but with a better build quality and vastly more FX flexibility. This is what the original AxeFX was based off of with its grid layout. Don't pay more than $450 for this. Make sure it's Version 2.04. No TRS channel switching, but does have SPDIF. You'll probably want a line mixer and set it to killdry, though.
* Old AxeFx Ultra, AxeFX II. Price varies. This is a 2u solution, though
Do not get the G-Major 1. Their encoder wheels break off like crazy.
Note that all old gear also comes with the price of it possibly breaking and there being no parts available to fix it. Biggest thing that happens is encoder wheels dying, power supplies dying, and screens dying. Some parts simply aren't available anymore.