I wasnt even sure what a Tavor was until I looked it up. The SCAR is definitely an awesome design incorporating a lot of cool features from almost every facet of the firearm world. Out of the box its cooler than most guns can get with all the custom parts you can throw at it. However, it still doesnt incorporate the size advantage of the bullpup. Honestly, I think bullpups are going to be seen a lot more in the coming years. I would go with the bullpup all other things being equal.
SCAR H, I need a 7.62x51... I'm not all that fond of the 5.56 round, and while bullpups look sexy... I'm more concerned about my rifles working for my hulkish proportions!
Which SCAR? The -17S is fairly unique among 7.62x51 semi-auto rifles. It is lightweight, accurate, ergonomic, versatile, and has relatively light felt recoil. The -16S, OTOH, is just another 5.56 bullet thrower in an already crowded field. IMO, of course.
Comparing the -17S to the Tavor is apples and oranges, and which one to choose depends on what niche you're trying to fill. Comparing the -16S to the Tavor, I'd probably go with the Tavor, but honestly neither rifle really interests me all that much.
Tavor. Full-length barrel in a compact rifle size without a need for a stamp. Also, fully ambidextrous, not just half-ambi. The Israelis build very nice weapons, and they're built to last.