First, I'm connected with Kirk Hunter Studios. I consult to Kirk and came up with the idea for Pop/Rock Strings. But I'm primarily a user of sample libraries who also consults to a number of sample developers (I'm a marketing professional and a former semi-pro musician, now just a hobbyist) in the development, pricing and promotion of libraries and VSTs -- I don't get compensated for posting and I don't make royalties on Pop/Rock Strings.
I own Miroslav and GPO (as well as Session Strings and some other string libraries). Being a KONTAKT library, and much newer than Miroslav (which was created back in the 90s before round robins), Pop/Rock Strings gives you scripting functionality and things like round robins that are not available in either SampleTank or GPOs player. Ftr, I find Miroslav is fun to have and useful for layering. However, I wouldn't compare it to any of today's KONTAKT string libraries that offer scripting, round robins, velocity layers, etc. I think of it mainly as a secondary or tertiary library useful for layering/thickening up lush string parts. Further, the technology for Sampletank is far less sophisticated than KONTAKT and the samples were recorded back in the 90s before developers were thinking about things like round robins, velocity layers or scripting (I own a ton of SampleTank libraries from IK, Sonic Reality and others and have been eager for SampleTank 3 to come to market). Consequently, I find the scripting and other capabilities of KONTAKT really make a huge difference, imo, if you're seeking to have a realistic string part whether you're talking about Pop/Rock Strings, Concert Strings II, LASS (which, imo, sound great too), etc. If you're doing disco or 70s cheese type Motown retro strings, Session Strings is a very good choice imo and should be in your consideration set.