I don't really have a favorite evolution method, I think every single one has its own merit.
Leveling up and High Friendship are definitely the better ones, though, if you ask me. They're plain and simple and easy to achieve. Stone evolutions are okay, too, but most of the time, I'm bothered by the fact all Stone Evolution Pokemon (or most) stop learning new moves after evolving, so it gets points down on that front for me. I'm okay with trade evolutions because prior to the Switch games I could trade between myself or ask a friend if I really wanted to have a Pokemon that evolves through trade to evolve. Now I can't though without paying a fee for a subscription so I don't use trade evolution Pokemon in the Galar games. (I might not in BD/SP, either.)
Time based evolutions are okay, too, I'm fine with them, but will often forget when a Pokemon can evolve. Like, I believe Budew can only evolve with High Friendship during the day, or something? It's pretty easy to just change the clock of your console/system to manipulate that, anyway, but it's not really an evolution method I think about often.
Evolving while holding a certain item (both level up and trading) is fine, too, but there aren't a lot of Pokemon that use items to evolve. I think only a handful have to hold an item to evolve. Sneasel, Gligar and Happiny, I think? Those aren't too bad, but from what it looks like, most of the time those items are locked to the post game. That's a little aggravating, if I'm being honest, and I wish the Razor Claw/Fang were something you can get earlier in Gen Iv, at least, anyway. But, Sneasel isn't available all that early on, anyway. Evolving while using a certain item is pretty decent, too, but is so much better than the evolutionary stone method.
Some of the evolution methods that require you to go to a certain location or know a certain move are the more annoying ones to me, if I'm being honest. Especially Leafeon and Glaceon, though. It required Game Freak to have to put a Moss Rock and Ice Rock in every single Pokemon game until they decided to change it in Galar, which I'm grateful for. Most of the time, the Moss and Ice Rock were in places you'd rarely ever go making it less likely you'll get to use Leafeon and Glaceon. For example, you can't even get Leafeon in B2/W2 until after the post game, which is really annoying. I honestly think this evolution method would be better off if they had the Moss and Ice rocks in multiple places throughout the region and not just one literal place on one map where you have to go find it yourself.
Which is why I'm glad that method is gone. It'll return in BD/SP, though, I'm sure.
Location based evolutions are a little annoying, too, because most of the time it is, again, only one location on the map. Like Nosepass into Probopass can seemingly only happen in Mt. Coronet in Sinnoh. I'm sure there are plenty of places in Sinnoh with electromagnet waves in them. I don't know, I just feel the specific location evolutions are just too gimmicky. It should just be anywhere with an electomagnetic field, which probably is not a lot of places, but still.
For move specific evolutions, I'm okay with them, but some of them are annoying. Did you know Piloswine can't learn Ancient Power naturally and the only way it gets it is through the Move Tutor? Some people probably don't even know where the Move Tutor is (in Sinnoh) and will likely miss an opportunity to evolve their Piloswine through that. Poipole, too, Poipole does not learn Dragon Pulse naturally, and you have to teach it through a Move Tutor. It's easier now that SW/SH plant a move tutor in every single Pokemon Center, but in older games we didn't have that luxury. There was only one move relearner in every region until Galar. This honestly makes the move specific evolutions more frustrating to me than cool.
And some the gimmicky Galar evolutions are a tiny bit ridiculous that I feel new players would not know about if they went into this game blind.
Like how am I supposed to know to spin my joystick to evolve a Milcery if I didn't look it up? It's a cute evolution method, don't get me wrong, but what if spinning is removed in generation 9? How will Milcery evolve then?
Same with Galarian Farfetch'd into Sirfetch'd having to get three critical hits in one single battle can be hard if you don't have that one specific Farfetch'd item that boosts critical hits ratio.
...And Galarian Yamask is so horrifically specific. Having to be below a certain amount of HP and be in one very specific place on the map? When I first heard about that evolution method, I was completely astounded by it. I can't even fathom how it'd work outside of Galar.
Other gimmicky evolution methods aren't that bad, though. I'm alright with Eevee into Sylveon and Inkay into Malamar. It's interesting to have to flip your console upside down after the Pokemon levels up. I wouldn't mind if they change Eevee to Sylveon into a Fairy Stone or something in later games, though.
So, most evolution methods are cool, and I don't have a favorite, but some of them just annoy me a tiny bit.
