I've used Essential Depot for well over a year exclusively and I've never had a problem with it. When I nail a mix I usually make a large volume so I won't have to mix repetitively. These large batches will last for 4-6 months or more and they usually get better with age. I have a Zoochberry Cream that's over a year old and it's still great.
As far as comparing VG by vendor... I haven't done that. Probably because I'm happy with Essential Depot and I've never had a problem with it.
I noticed in the majority of your mixes you use common flavors and in some you use EM (known to kill flavors). The culprit could be with your flavor choices and EM.
I've only tried a couple of your mixes and they seemed a bit week to me and they didn't improve with steep. More than likely they just wasn't compatible with my taste in eliquids... (Flavor subjectivity) because the 2 I tried has a huge following.
Just my opinion.