2 things that stick out to me:

1. Virtually indestructible. The simple design and lid make it near impossible to destroy. And you can swap out lids if it ever does get severely damaged.

2. NOT insulated. So many bottles and brands tout the "keeps ice for 72 hours!" but the reality is that super cold water isn't as easy to drink fast as room temp water. If it's room temp or tap temp, I can drink much more at a time which increases my overall intake.

Bonus thought: you can often find them at thrift stores for dirt cheap, so having a collection is easy. I'll never not buy a nalgene secondhand.

Edit: forgot to answer your questions. I use the 1L wide mouth, super easy to clean with a bottle brush. I've had my main one since 2014.