I have both, and honestly, while both have been excellent pick-ups for me, I use both for very different aesthetic goals (also, I use both in conjunction with "sister" libraries - Sonokinetic's Orchestral Divisi Strings for MSS, Audio Imperia's Areia for TSS). So I'm going to write the rest of this post with the assumption as if both of them are equally aesthetically pleasing to you (although I will touch on certain things tone-wise anyways). Also, keep in mind that this is only how I approach and use them - I'm certain I haven't even started to get close to use either of them to their fullest potentials.
MSS, while it's full of content and has advanced features (not to mention allows you to write in Divisi), it needs work to get good results out of it. Nothing you can't learn (I'm still learning myself). I would still be very hesitant to suggest that it's a good fit for someone starting out, unless I'd know that person is willing to put in the work and is ready for the learning curve. Not specifically because of the features, but because of the tone and room characteristics. Those can be somewhat overwhelming (or "boxy" as people like to describe it). And even if you really like the sound out of the box from the examples you've heard - once you start adding instruments on top of each other, it can be a bit much, so I feel that it's good to be ready for some carving to make everything sit nicely together. At least from my perspective, MSS is this box of thick clay, and you have to carve out your desired sound from it. Also, while MSS does have the auto-divisi feature, and while it can be very nice (especially for the shorts), for certain things I'd still recommend to use the A and B sections separately, for better dynamics control.
TSS, while I've had it for a shorter amount of time, feels like it's easier to understand how to use & get it up and running, both feature-wise and tone-wise, so it would make more sense to recommend to a beginner. Not quite as feature-packed, but it's still a very good and comprehensive library. Similar story with the content. But if MSS's sound needs to be carved out, TSS to me feels more like you need to space it out a bit due to its nature and add to the sound of it for it to shine (a good reverb I feel is a must, even though you do have access to some of them in the library itself). One thing I'd point out is that out of the box, the library is configured to have very little dynamic range - that's something you need to increase via the interface if it'll feel too tight.
Neither of them are "quick and easy gratification" libraries with pre-produced sounds out of the box, but to me, TSS is probably a bit easier (or at least faster) to get to a good state. You do need to somewhat know what you're doing with both. For example, with MSS, usually the first thing people learn is that it's a good idea to turn the built-in reverb and EQ off, and then proceed from there. Both have quite powerful engines which allow you to modify and tweak quite a lot of things, so they're versatile. If you end up preferring to use mic positions over pre-made mixes like I do, both can take up quite a bit of RAM if you're not careful. However, both have ways to help with memory management.
Both also have planned & teased upcoming updates which will, apparently, add, enhance and refine quite a bit, but I'd advise from buying based upon "promises of the future".
Now, if you're looking for a more close-up, intimate feel of the strings, I'd say that both will do just fine (MSS has nice close mics, TSS is studio-focused, both can sound "smaller but full" and thus more focused than a lot of libraries out there). Both can then be shaped pretty well into other sound profiles (people have posted on how to "westernize" TSS so it can be used outside of its comfort zone, as well as tips and tricks on how to tame MSS's tone). Both, if used properly, can be shaped to the point where you can place them rather convincingly into different spaces (or at least, close enough). Both have pretty aggressive-sounding high dynamics that should be used sparingly.
MSS does have an upper edge where its Divisi feature lets you go smaller or larger, while with TSS you'd need to use the transposition trick or layer it with something else if you'd want a larger sound.
Yes - as you say, either programmed in via piano roll or played in via MIDI controller. Personally, I'm not a huge fan of using the various versions of the Auto Rhythm Tool in MSS, but YMMV. Such tools can surely save a lot of time, but I'm just not happy with the results.
Unfortunately, with sample libraries, you won't truly know how well it fits your desired aesthetic and fits your needs until you try it out for yourself. I hope you find at least some value and food for thought out of this comparison. Good luck with your choice!