The pro controller is significantly better for the comfort of adult hands. The sticks are just a little too long though, so the travel is a bit far. Might want to look at third party versions.
Also helps that the pro controller actually has a d-pad. I get why the joy cons do not have a dedicated d-pad (for when using a single joy con as a controller), but it is terrible when playing certain games, like Mario Maker, in handheld mode.
To contrast this, I found that I much prefer to play Celeste with the joy-con buttons. The Pro's D-Pad is mostly excellent, but it seems a bit too eager to trigger diagonal inputs, which in a tight platformer like Celeste is typically a death.
Of course, the left Joy-con still has those signal disconnect issues...
There's a fix you can do if you want to open up your pro controller, basically putting a bit of tape on the lower 3rd of each d-pad sensor helps limit those accidental presses.
This is true, and I have one and it has much better signal too, but I prefer joycons still. I like having independent hands for both comfort and also the motion controls in Splatoon (which are honestly better than a mouse) make more sense to me with an independent hand than joined hands if that makes sense.