I have owned the PSB Stratus Mini and the PSB Platinum M2 bookshelf speakers and also the Silverline SR-11s (twice). The SR-11s were the winners in my system, by a lot. They have a much more natural sound, a bit laid back but with a very real soundstage. The PSBs seemed flat by comparison.
I have never owned the SPB Imagine bookshelf speakers.
If you are looking for used, the SR-11s currently listed seem a bit high priced. One more thing about the SR-11s, be cautious with the black lacquer finish. I had a pair in the red lacquer with a superb finish, but the pair I had in black had a poor finish.