Ive had 4 of them from three manufactures (ultimate direction, Nathans, Salomon). Get the Salomon advance skin in what ever storage size you think you need and don't look back.
I have an older Ultimate Direction Mountain vest. It's about 12 liters and holds everything I need for most day hikes/runs. I recommend getting the soft flasks with the longer nozzles. It makes drinking with the bottle in the vest easier.
Kind of depends on what your use is. For longer stuff in the mountains (where you need to carry a little more) the UD Mountain Vest or even their smaller Fastpack work pretty well.
I use the Nathan vapor krar it is light and comfortable, I use the 14oz flasks with the long tubes. I also have the osprey duro I use a bladder with, I like it but it’s a bit overkill for most runs, I’ve heard great things about the Solomon adv skin. I tried an ultimate direction race vest and it dug into my back and caused some bad chaffing. Probably works great for others.
For trail running, I use the Salomon Advanced Skin 5 for nearly all my longer runs. I also have the Salomon Advanced Skin 12. I use the 12 for all day, self supported trail runs in the mountains. I use them both the same, just carry more stuff in the 12. I'll carry up to 4 full soft flask water bottles, a filter, rain jacket, extra layers, food, etc. in either. My 5 has one zippered pocket on the front, the 12 has two for whatever you don't want to lose. For the most part, the all pockets are all pretty accessible without taking the pack off. They both ride really well with virtually no bounce. There are also bungees on the outside to strap down additional layers or trekking poles.
I also have an Innov-8 pack with a removable pouch. It's a decent vest, but it pretty much just hangs in the garage in favor of the either of the Salomon packs. I've also run a bunch of miles and races with an Ultimate Direction vest. It was a decent vest. But it got perma funk, so I started shopping for something new. That's when I got the Salomon AS 5.
You won't go wrong with the Salomon vest for running. I'm happy to answer any specific questions if you have some.
I have used Ultimate Direction for years and they have worked great on some really long stuff. I have not used any other packs so my sample group is 1.