I don’t have any unifi kit myself, but am running pfSense on my router.
I’d recommend pfSense, as it will give you the most flexibility if you bought your own box to run it on. You can also just buy a netgate device too.
Either way, you can also simply install pfsense in a vm and setup virtual networks if you really want to. However, you will probably get more problems to solve if you are running pfsense on your main router.
I’ve done both and have to say my virtual network is just there unused, I couldn’t actually get it going when I first started with pfsense, I had to play with it on physical hardware to understand it personally.
As for future proofing, I believe Cat6 is the minimum to run 10G, that’s at least what I did. Cost for 10G is still eyewateringly high, I hate all these crappy intermediate speeds. That’s the best you could probably do now. However, there is more kit becoming slowly available >1G<10G so you have a choice, but I’m waiting until I have a real need and prices come down on 10G.
I’m just paralyzed thinking about the difference in price between Dream Machine SE and the Netgate 6100/8200 hardware. I have the $, but I’m not sure whether “a fool and his money soon go their separate ways.”
The UDM has certainly added many of the features they were missing but it really comes down to your needs. Just because you have more control and more options in pfsense it really comes down to will ever use those features as most people do not.
The netgate box will do a little more for you in this regard. Unifi has a “Fisher Price” feel to it. But my feelings aside, it can absolutely work if you never want to go beyond a one or two hour learning curve. IMO pfsense is only modestly further out on the learning curve anyway.
You also asked which one will help tech you networking. IMO, using PFsense will do a lot more for networking skills then Unifi ( to add onto what @liquidjoe mentioned). However I do not feel either will really give you a good learn to network experience. I cut my teeth originally on Cisco IOS where there is no guidance from the system, you have to learn and do. These systems, Unifi and netgate are great, for usability and management, but i feel as if learning networking on them wont really give you the experience.
@LTS_Tom pointed out to me on another thread the 6100 (which i am still setting up) doesnt come with a built in switch, so for pushing out the vlans, you will need a switch that can trunk them together. My rambling point is that, pfsense and ubiquiti do things a bit differently. So it all depends on how much you want to learn. But as @LTS_Tom said, you will be getting a lot of features in PFsense you will probably never use, but they are avaiable if you want to learn.