I just answer the initial question, I do not say one is better than the other.
But I currently have a VSR10 Full PDI and a SRS 16" Push, and my preference goes to the latter, more solid, simpler, very well thought out, I really like to play with.
But it is a purely personal feeling.
My Wolverine Bolt is almost finished, we will see what it gives.
For the hop-up chamber, the original is very good but it is really quite boring to settle.
A new hop-up chamber come this week, with fast setting, big window for R-hop...
Silverback Airsoft SRS F.A.S.T. Hop-Up Unit | Popular Airsoft