I’ve been flying CRJ since first release on P3D. In my opinion is beautiful looking plane. Handling is really good is quite agile and flies more like Citation than 737. Engines are rear-mounted and interesting wing characteristics which is making it very slippery bird its quite hard to slow it down. Has natural tendency to rise nose when you pull back power which makes landing very interesting. If you bang on speed and profile on approach once you close throttle you may not need to flare as she will settle nicely on tarmac by her own. Also is quite easy to over rotate on flare and can float forever sometimes you even need a little push to get her down. Once you get used to it landings are very satisfying. As mentioned above its regional jet so is smaller with smaller range than others and mostly used for short routes often to small regional airports. If you are using something like Pilots life go for Iberia you will have interesting and challenging approaches. System wise is not as automated as Boeing or Airbus. Doesn’t have A/T but it has some throttle detends for climb and toga which makes it easier to manage on takeoff and climb. Its climbing nicely but is losing loads of performance above FL300. Its mostly cat1 and sometimes cat2 rated for ils but quite often you will shoot visual or circling approach (Pamplona is great) on small airport. With lack of automation is very busy plane to operate. FMC works well and easy to set but has some quirks ND is clear and easy to follow. It has quite modern cockpit which I found much nicer and easier than 737. Has also modern features like EICAS that making life much easier to find out whats going on and Nav autotune with that is winning with 737 in my opinion. Real crj drivers saying that it flies very close to real thing but system simulation is lacking a bit. Is not as detailed as pmdg or fenix. Is giving you what you need to perform full procedure flight but some switches are not doing much. E.g you can turn off all hydraulics and still all system works, you can still taxi with nose wheel steering off, start engines with fuel pumps off etc. You have EFB so all settings ground services and perf calculation are easy to do. Aerosoft promised some updates so I guess it will get better with a time.
737 is completely different plane. Much bigger much heavier and in my opinion much harder to fly than CRJ. Its like sports car to family van. Engines are mounted under wings so is giving you opposite characteristic than CRJ is rising nose when you give more power and dropping heavily when you reduce drastically you need work much harder on flare to get her nicely on tarmac. But its quite rocket ship with climbing rate which makes her hard to control if you have SID restriction on some 3-4k. System wise is more automated than CRJ you have full Vnav, A/T loads of MCP modes to learn but boeing has not change much since beginning and cockpit looks complex and overwhelming its modern very automated plane but seems a bit like from 60s. Displays are not as clear and informative like in CRJ in my opinion but automation is doing loads of work for you. Its very popular so again if you are using Pilots life you will find plenty of routes to do. Simulation wise according real pilots that opinion I heard its state of art. Flies like real thing (with msfs limitations and quirks) but best thing is system simulation. Is very detailed and you really need to know what to do to operate this plane to avoid nasty surprises and “what the hell this plane is doing”. If you forgot about something it will bite you not like with CRJ. E.g fan is not spinning on engine start you forgot APU bleed, you get waking alarm on climb probably packs or press on manual. Failures simulation to very deep level where without QRH you lost. Overall 737 as simulation is more complex and more detailed than CRJ therefore much harder to learn but really satisfying once you get there and is always something to explore and push yourselves to extreme situations with failures simulations. It lacks EFB but is still easy to operate with FMC. Performance calculations is biggest problem but is couple good tools that helps with this.
I can’t say much about fenix as I’m not big fan of airbus. I was flying one in P3D just to explore. Flies similar to 737 but is massively automated and in most cases plane tells you what to do. ECAM is a great thing that 737 lacks in my opinion. Has really easy cockpit to follow but more systems to set than Boeing. Once is configured properly it flies alone pretty much. Fully FBW you don’t need to trim it so I’m finding it a bit boring and I prefers yoke than sidestick. But what I found as home-cockpit single pilot environment Airbus is much easier to handle but still much complex to learn than CRJ. Based on what I’ve seen about Fenix is as detailed if not more than PMDG.
Its really how much time you invest because each of them are not jump and fly and if you are seeking realism you will have learning journey in slightly different direction with each model.
Below few videos I found interesting that will give some view what you are getting into:
CRJ
737
Fenix - whole chanel I found interesting about fenix
One more for 737 very good tutorials
https://www.youtube.com/@737NGDriver