Mmm...all soungs pretty good to me. Balsamic is fine, but there are so many of them and they vary so much in quality - a really fine aged balsamico di Modena can be so wonderful but I have also encoutered some rather poor ones. Olive oil, likewise, is such a big subject and these are now produced in and exported by so many countries - Crete is quite a large producer of it, despite being a small island, but in UK today one can also buy olive oils from South Africa, Greece, Italy, France, Spain, Australia, New Zealand and all manner of places - so finding a really good one, even among the cold pressed organic extra virgin variety, can be quite a challenge and, of course, different olive oils and balsamics work in different ways in different dressings and many other applications and uses. Other oils can also work wonderfully in salad dressings, not least a good French walnut oil.
There are surely limitless combinations of ingredients that can work successfully with that basic one of olive oil and balsamic to make a good dressing; I often put finely chopped fresh herbs of one kind or another in them, mustard (as has been observed) can work really well, lemon juice can work as a good alternative to balsamic, the sugar or no sugar argument is one on which the jury must forever remain out, I think (and for those with an aversion to sugar in and/or out of cressings, there's always the alternative of honeys of one kind or another).
I've never had the apparent misfortune to taste what you call "ranch" and have only ever bought a ready-made dressing once (most of which went down the waste disposal - never again, thanks). What's important at all times when using a salad dressing, however, is that it always only complements and but never swamps what it's being put on...
Best,
Alistair