Of the two Sicario films, the first is most certainly the better, though, in my opinion, not at all by the margin that I have seen many others imply. These are both great movies, not great in an identical way (even if their formula is identical) but both great. I don't know that Sicariohad to be a film series as opposed to just the one movie, but the best experience I've had at the cinema for the past couple of months was with Day of the Soldado, so I'm glad it became one.
Final rating:★★★½ - I really liked it. Would strongly recommend you give it your time.