I too have been running in ill-fitting hydration vests for the past couple of years, and the Adventure Vesta came highly recommended by a few friends so I figured it was worth a try. Also, I bought the Adventure Vesta based on the liter capacity, simply because I'm often running with my dogs and having that extra space for a first aid kit or extra water for them is a big priority for me.
The Adventure Vesta is comfortable, lightweight, and has a myriad of storage options which makes it an ideal companion for long runs. The mesh is soft (so it won't chafe), super breathable, and dries quickly. Additionally, the shoulder harness is designed to ensure maximum mobility, which is rather ideal when tackling varied terrain. The wide straps are especially nice, though sometimes I wish the pack-panel-to-shoulder-straps-ratio was a little more even-keeled and complemented each other. Sometimes I feel like the Vesta could be a little wider on the pack side of things.
The adjustable chest straps are a huge plus - and they're stretchy. The pack features side rails that you can slide the chest straps up and down on, so you're able to customize your fit based on chest size or preference.
The drawcord at the back doubles as compression - and there are actually these neat little plastic hooks (just beyond the outskirts of the cinchcord at the back) that allow you to really batten down the hatches.
I love the soft bottles design - they're easy to take in / out of their respective holsters, are easy to pack down, and provide fast hydration. My major issue with these soft bottles is that they are a little leaky from the lid - I speculate this might be a bit of a defect, because I have a UD soft flask handheld and have no problem with leaking (with that one). That being said, I'm far from bothered by the moisture - it sometimes can be a nice reprieve on hot runs. The pack does feature a hydration sleeve (for a bladder), which is convenient if you're running with dogs or doing an extra long run.
I really love the variety of storage options, simply because I'm a bit of an organization fanatic. Especially on long runs, I like knowing where my stuff is - the whole frantic fumbling through my pack for an extra layer or fuel really sort of drives me crazy.
That being said, I was a bit on the fence with the Adventure Vesta when I was originally purchasing it. Namely because of the adjustable hook-and-loop (which is another term for velcro) detail at the side, which is designed to make fine-tuning your fit easier, but I'm honestly kind of worried about the longevity of this detail. However, I have gotten it wet and it stayed attached, which I was also worried about (it not staying attached, that is). I really wish that the Adventure Vesta featured a hidden and adjustable webbing strap (at the side) like the AK Mountain 3.0 Vest has. That would be pretty stinkin' perfect.
Occasionally, I do feel like this vest is a little overkill for shorter runs. But at the end of the day, I like having extra space for dog-necessities and fuel / layers / etc -
especially considering the fact that I don't race, but still run long distances (so see ya whatever aid stations may have been there). It's nice to be able to carry what I need and not have to think twice about it.