If you want a monosynth you could go with…
…Moog Subsequent 37
…Moog Grandmother (less bells and whistles than the subsequent but sounds amazing to my ears)
…Moog Mother 32 (most limited Moog from this list, nice Oscilator though)
…MFB Dominion 1 (a BEAST of a monosynth)
…Dreadbox Erebus (for Bass and Leads)
…Dreadbox Nyx (for Leads and Blade Runner type pads/atmospheric soundscapes)
If you want another polysynth you could go with…
…Behringer DeepMind (not really my cup of tea but some people love it)
…Dreadbox Abyss (4-voice poly only but Dreadbox makes awesome synths)
If you have money to burn…:
…Sequential Prophet X
…Moog One (lol)
If you want four monosynths or a great 4-voice polysynth for pads, lead work and atmospheric madness…
…Elektron Analog 4 (I can’t get good bass out of it, but for everything else it sounds great to me)
On to some general advice:
Your Rev2 has a particular sound (that aggressive, fuzzy DSI/Sequential sound) that in a way is the polar opposite (relatively speaking in synth terms) to anything Moog (“rounder”, deeper…). So if you want to go for diversity, maybe don’t get a Pro2 (which is awesome also!). Of the Moogs, the Subsequent is somewhat more aggressive sounding (or capable of it), while the Moog Grandmother is semi-modular (hence: you can patch its parts into each other in almost any order you like, allowing for very interesting and unusual sounds) and has a lush sounding spring reverb integrated…the MFB Dominion 1 has its own sound entirely, and is really a great monosynth all around! Check out Nick Bates’ review on SonicState (YouTube) to get an idea of its sound (or watch Nick review any of these other synths also).
The Dreadboxes are both fairly cheap (especially the Erebus - and even more so if you buy used) and sound fantastic, with their own sound also. The Erebus is creamy, very “analog” in sound, with a notched filter that can go mad if you want it to. The Nyx has a splash mono reverb integrated which just does something to the sound that pushes any patch into Blade Runner territory!
With the polys I listed…well you can’t go wrong with either of them, but you already own a Rev2 so not sure if you need another…if I had to choose a SECOND POLY for you, I’d get you a Digitone, as that’s FM synthesis and thus is capable of different sounds (and sounds different) than your Rev2.
If you have money to burn and want a Rompler (read: NI Kontakt in hardware form) that can do lots of different high quality sounds (strings, piano, outthere…) the Prophet X is a beast…but so is its price.
Lastly the Elektron Analog 4 IS amazing and it is exactly that combination of sequencer and 4 voices that can all be sequenced independently(!) that makes it so powerful. As a synth the A4 is very deep. And the Elektron sequencer is obviously the bomb, even for chord/harmonic sequencing (4 note max per step, which is limited but works out perfect with A4’s capabilities). In a harmonic scenario, the p-locks really can spring chord progressions to life by bringing movement and diversity to the chords’ sound (you can also do this stuff with an LFO, but p-locking allows for more/different control).
Have you listened / played with any of these synths in person? If not you should really do so. It’s usually the combination of sound, features, user interface / user experience design, and the personal “Oh damn I feel this” factor that make a synth great for you. The greatest synth is no good if its layout doesn’t inspire you to program and play it.
Also you should really think about what the purpose of each piece of gear you want to acquire is! Otherwise you can quickly get paralysed by all the options out there (or buy three boxes that excel at the same thing but offer no variety).
It’s hard to give you a specific recommendation when you only ask “which one is better?” because it all depends on context and purpose for the most part. Eg “which is better for bass?” or “which is better for orchestral scoring?” will still not produce absolute truths but maybe a little more specfic & hopefully useful answers
Hope this helps.