Among the zooms you mention I used to own the 70-300 IS and now own the 70-200 f/4 IS L and 70-300 L. Perhaps I had an unusually good copy of the 70-300 IS but while the 70-300 L does provide superior images, the superiority isn't glaringly obvious, and I bet it's far superior to your Tamron ultra-zoom at any length where they overlap. The 70-300 L is, however, plainly superior from a purely mechanical point of view - it's quite superbly made, has excellent stabilization and on my 6D never hunts for focus unless it's so dark I can hardly see what I'm trying to focus on, and even then it usually gets it right. The 70-200 f/4 IS is superb too, but I don't think I've used mine since I bought the 70-300, largely because I use the 70-300 at 300 a lot for background blur - 300 does that better than 200. Coming from APS-C, depending on how you used your Tamron superzoom you may well find yourself limited by a 70-200. If you doubt you'll want to go beyond 200mm, toss a coin between those two.
(I've only rented the 100-400, and maybe the copy I rented wasn't a particularly good one, but it didn't seem quite as good to me - mechanically or otherwise - as the 70-200 f/4 IS or 70-300 L, and I actively disliked the fussy bokeh it conjured up on busy detail fairly close to the subject.)