I've been to both for 3 nights each - quick thoughts below
1) Food - Saffire does win (it is superlative, my wife is no nuts / no meat and they rewrote a tasting menu for her rather than just taking out the nuts / meat) but SOL isn't bad either and will happily customise rather than just offer you the second menu - we certainly had a fantastic time eating there.
2) Interior Design - Rooms at SOL probably just win on this one - Saffire is great and we were wowed by it (having already been to SOL) but SOL has a little bit extra. To be honest I don't really value this one particularly and am not an expert... Didn't get the private pool so can't comment on that piece.
3) Things to do - here I'd probably rate Saffire over SOL. SOL has very little to do beyond strolling along the beach if you aren't doing one of their 'official' excursions. We did 1.5 days of official excursions at SOL and felt like if we'd just done 1 day we'd have seen plenty. Saffire you can go hiking on your own and are a bit more able to do other stuff.
4) Ease of access- from MEL you can surely fly direct to LST? Whereas for SOL you need to go via Adelaide from which its a further ferry / flight?
5) Other things. At SOL all the rooms are on a corridor so I think if you go for the nicest/ 2nd nicest room (can't recall which) its probably a 10 minute round trip to your room to get anything that you forget if you're going to lunch and then out on an excursion.
I'd pick Saffire but YMMV and neither is a bad choice.
Paul