Since Tesla supplies the 14-50 adapter with the car, but you have to *buy* the 14-30 adapter (which Tesla charges quite a bit for), think about that when pricing out your install.
Always get the 14-series outlets; everything else is considered obsolete.
If your breaker box doesn't have room for a 50-amp circuit, though, you may want to put in the 14-30 circuit. Otherwise I'd put in the 14-50.
The 14-30 adapter for the UMC Gen 2 is only $35, so not a ton.
As others mentioned, there is nothing wrong with the 6- series either. It is actually more optimal in some ways because it does not have the wasted neutral wire (the UMC will make zero use of a neutral wire on a 240v circuit).
If your breaker panel physically has the space for a 30a 240v circuit, then it also has the space for a 50a 240v circuit. The question is whether the load calculations will allow it based on all the loads existing on your panel / electrical service. Note that a 30a circuit would be calculated as a 24a continuous load. A 50a circuit on a 14-50 receptacle would only be calculated as a 32a continuous load since the UMC Gen 2 can only draw 32 amps. So even though the circuit is capable of up to a 40a continuous load, the load calculations are done based on the intended device to plug into it. Technically you could put the 14-50 on a 40a circuit for use with the UMC Gen 2, but I would never recommend that for a new install.
Here are Tesla's instructions for installing a 14-50:
https://www.tesla.com/sites/default.../NEMA_14-50_installation_guide_NA_US_2017.pdf
That makes sense, although if I were designing the code I would have assumed constant current.
Ie a 40A circuit should be able to handle a sustained 40A.
The code has decade upon decade of tweaks over time. I personally think it is vastly over-complicated at this point and could use nearly a complete re-write, however, that is very unlikely to happen. All the weird rules and tweaks that have been made have either been due to dangerous situations that needed to be addressed (i.e. fires), or because the rules were overkill and so there has been pressure to trim safety margins back where they were excessive (and that is why we get weird rules like the one that allows us to under-size a main residential electrical service by 17% compared to the standard calculation in some cases).
Note that the reason for the 80% derate on circuits handling continuous loads is because the extended duty cycle causes the wire and components to heat up and does not give them time to cool down. It makes sense to me that a stovetop that only operates for short periods of time could have smaller wire than an EV charger that runs all night at the same amperage. Specifically, the main issue with continuous loads is that the breaker can heat up beyond the "standard test conditions" it was tested under and it can thermally trip when you don't want it to (nuisance trip).
I recommend you read some of the dozens and dozens of threads here about what to do for home charging. There is a lot of info available.
I personally am a huge fan of the Wall Connector myself (especially since my car is parked outside), but everyone needs to make their own decisions about their needs and how cost sensitive you are (I like keeping my UMC in my car with me at all times in case of emergency).
If you post pictures of your electrical panel (and the areas you would need to run lines in and where you would install the receptacle or wall connector) we may be able to give you some idea of your options (how difficult things might be).
