It has some support for ostinatos too but it seems kinda simple when compared to the SSP2 (granted I didn't spend much time in the ostinatum section of this library). Lots of articulations allow you to express pretty much any musical idea in a natural way (as long as you spend hours of your time tinkering with midi and automation. Spitfire Solo Strings is my current go-to library for quartets. Very few articulations, though feels limiting once your sketch is laid out. What I like is that strings sound very natural and smoothly mix with my own violin recordings. Truth be told, nowadays I know how to do that in my DAW so it wouldn't be a selling point for me anymore.
It mixes woodwinds with strings based on the velocity and you get two great starting options at one. The British Drama Toolkit is a great idea for quick sketching. Here's some Spitfire stuffs (and I love Spitfire!) the smart voice split with the smart chord allow you to play the whole strings section with a single octave of keys – and play them nice! Rhythm and phrase animators are also kinda unique and allow you to tinker with ostinatos easily. It's a great library full of various features that can make your life simple e.g. I really tried to like it but it just didn't work with my way of composing. Session Strings Pro 2 is a curious beast.
Wouldn't really recommend this as a solo strings library. The Symphony String Ensemble sounds okei but I found the list of its articulations quite lacking.
They don't give you much in terms of flexibility but they're the most natural sounding libraries for short phrases – mostly because the way they were recorded. If you're fine with a few pre-defined phrases definitely go for Action Strings / Emotive Strings. Given the Komplete pack, here's what you can find inside: I got my hands on a good bunch of the strings libraries here are a few ideas. It kinda depends on what your playing style is.