Agreed with above that when it comes to shoes, trying them in person is essentially a must and sometimes I’ve even found that to be inadequate, with issues only showing up later when I’m wearing and walking in them for a longer period of time. And I can confirm that batch difference exists: I have found Hermes shoes of the same style (same material same everything) from different years sized differently, and needed a different size when I tried to get a second pair.
Out of the 3 you mentioned, I own Paris and Royal and find both to be quite comfortable. I do have narrower feet though and I take the smaller end of my normal sizes in both (I’m size 36.5-7 depending on shoe and brand; these I need 36.5). The Colette reportedly has less secure hardware with reports of the hardware falling off, which is why I have not purchased them.
The most comfortable pair of H loafers I own is sadly not in production from what I can tell; it’s the Ancora loafers without any decorations and just plain leather. The soft leather plus lack of hardware is what made it the best in terms of comfort for me. The hardware can put downward pressure on the top of your foot. If you have tall ish feet that may be something to keep in mind, although I’ve found that in some shoes that pain goes away after I’ve worn them for a while so they can get broken in. This is one of the things I sometimes don’t even find out when quickly trying shoes on in store (probably don’t walk enough for the downward pressure to manifest itself) and only experience it later when I’m wearing the shoes out for the first time.
A side note: for all these shoes, creases will develop at the top of the shoe in the part that gets bent when you walk, naturally and inevitably. I know people who are a bit bothered by this, in which case the royal loafers imo has the least obvious creases (but it will still have them!) thanks to the fringes design.
Anyways, I cannot recommend trying shoes on in person enough! These styles should be pretty easy to find in store (although maybe not in the exact color / size you want). If you can, definitely do that first!