I carry 3 sizes:

1) One 32oz widemouth Nalgene bottle
2) One 14oz Nalgene bottle
3) One 64oz collapsible bladder.

The 32 oz (1 liter) bottle is the main workhorse. It goes in the accessible, outside pocket on the side of my backpack for immediate water on the trail.  I also use the 32 oz at night for a hot water bottle in my sleeping bag.  Yes you can pour boiling water in your Nalgene and it will be just fine.  If you’ve been doing this for a while, you may want to make sure your old bottle is BPA free. Be sure to have the lid on tight. Leaky, badly sealed bottles are a pain, leading to wet clothes, or food. Not pretty!

As with all gear, if you find a solid product that works for you, go with it and stay with it! Nalgene wide-mouth bottles are a great example.The 14oz is my coffee cup in the morning and my tea and sugary mix drinks on the trail.  It fits in my pocket for a hand warmer on cold mornings and is easy to carry for route scouting when I drop my pack. The 64oz collapsible is for in camp use.  They weigh very little, take up minimal space in my pack. In camp and at mealtimes I always find is a nice time to share your filtered water around the camp.  I always fill all of my bottles the night before so I have enough water to make breakfast and hit the trail without having to break out the filter again in the morning.  On hikes that will not have a lot of water I use the 64oz as my additional water container on the trail. I refill the 32 oz bottle from this along the route. If I am hiking with a less experienced backpacker I would likely throw in a second 64oz collapsible.  I prefer to make all of my water at one time and for the small amount of weight and space, it usually proves helpful.

Staying hydrated on the trail is paramount to a great hiking experience. Comfortable, accessible water containers make that an effortless experience.

Happy hiking!