I would consider that entirely personal preference. Whatever works best for you. Some people may have physical limitations why they cannot use hydration packs. I like using one on longer and hotter rides because I drink more that way. For shorter rides I do just fine with bottles.

Making fun of hydration packs on club rides? Hasn't been the case on the club rides I've been on, but I guess that would depend on the club.

And if horse poop, goose poop, or other poop were a risk on my rides, that would certainly fall in the "pro" hydration pack arguments!