The last time I held an Old3DS was when I was 11 years old, so I don't know.
Also holy crap, the 3DS has been out for 9 years and it's still technically supported.
The only reason the old3DS feels more comfortable is because it's slightly smaller, and doesn't weigh as much. Otherwise the 2DS is the most comfortable despite its shortcomings.
I honestly prefer the n3DS, but I never got to own one. I've had the same o3DS since around 2013, although I always wanted to upgrade, but they got discontinued and I'm not a huge fan of the n3DSXL..
Oh... in that case 2DS all the way. I hate the GBA SP -style buttons, although it's really easy to press on my new3DSXL. But despite the difficulty of the press, it does indeed feel really good on the old3DS, but it starts to hurt quickly.
Also holy crap, the 3DS has been out for 9 years and it's still technically supported.