Mostly been playing handheld but other than that I'd say Joycon+grip.
Yet to pick up a Pro Controller. I haven't tested out the Gamecube controllers for the Switch yet either

Okay, I've managed to make the console detect the GC controller, but I can't get it to work as Player 1. Any suggestions?

I like the Pro Controller, but 90% of my Switch time has been in handheld mode, so I bought some Silicon Hori grips for my Joy-Cons, and they actually feel really comfortable.

The Pro controller is amazing, the joy-con's are utterly worthless for me, regardless of how I use them. Using the Switch in handheld mode is really uncomfortable with the controllers slapped on the sides, my hands and arms go numb after a short while, the trigger buttons are too shallow and lack feedback and the buttons are too small and too close together and make your thumb hurt.

This one:

Is this real?

And old. It's a mod from the launch period.
https://www.reddit.com/r/NintendoSwitch/comments/5zlbo2/my_dpad_joycon/

Plus a better one with more details:
https://www.reddit.com/r/NintendoSwitch/comments/6gdsal/my_attempt_at_a_joycon_dpad_mod/

Ah, Nintendo really needs to make a left joycon with a proper d-pad already.

That would literally go against the core concept of the Joycons being symmetrical for duplicating controller purposes.

The Pro Controller is God-like. It's so comfortable.