Sorry if this is a lengthy post but...
I have been into photography for around two and a half years now, and have made some big (for a 17 year old) investments into my equipment, and I am currently looking to make a much larger one than I have so far. I have saved up around $1200 and I have narrowed my search to two things: either a 70D, or a Tamron 70-200 f2.8 di vc usd.
I started in the hobby when I got a T2i. I used my dad's old tamron 28-80 f3.5-f5.6 and his tamron 70-300 f4-5.6 that he used on his Elan 7E for around a year until I got a 17-40 L and I discovered my aunt's old pentax-k bayonet 50mm f1.7 (which I absolutely love). I most recently got a canon 28mm f1.8 (which I also love; contrary to Bryan's review...) but I have come to the point where I am looking to upgrade from my t2i as well as my 70-300.
I'll start of with the reasons I feel that the t2i is not performing as well as I would like and why I feel the 70D would help:
The 3.7 fps is a very limiting factor for me. I could often use a faster burst, especially when shooting the football games ect. at my high school. The upgraded autofocus system of the 70D would definitely be a big help as well. The improved IQ and ISO performance (albeit a small improvement, but an improvement non the less) would help since I like to shoot the plays and performances at my school, and since long exposure photography (specifically night-scapes, star trails, and steel whool) is one of my favorite things to do. A less important reason is that the 70d has many more buttons, menus, options, and customization ability. I know the amount of buttons is not a big deal, but I love pushing buttons... Anyway, I have pretty large hands, so the bigger 70d would help there as well (although my battery grip does a great job at helping that). One big upgrade is of course the dual pixel af. I primary shoot photos, but I enjoy making videos quite a lot, and since I am involved in many clubs, I am constantly making short promo videos where the autofocus would help greatly. I also am trying to shoot a short film this summer, where it would help too.
Now why I want the 70-200:
As I said earlier, I enjoy photographing football games (just about all of which are at night), and plays and such, and in those very low light situations and f5.6 lens simply does not cut it (partly caused by the t2i's not so great low light performance). For most of these events, I have borrowed my uncle's canon 70-200 f2.8 non IS, and I love it. The image quality is awesome, and so is the build and autofocus, and it most importantly has that f2.8 constant aperture. The added light over f5.6 is immense. Since I would love having IS, $2500 is way out of my price range, and the image quality is not much off of the canon IS version, not to mention the very comparable IQ compared to the non-IS version, I settled on the new tamron version of the 70-200. I am interested in shooting some of my friends informal senior portraits, and since I don't really have a lens that is very great for portraits, the 70-200 would fit well for me.
Now for the downsides of upgrading to the lens rather than the camera:
The lens is nearly $500 more (especially with the very tempting deal on the 70d that B and H has right now...), and $500 is a very substantial chunk of cash for me (I got my 17-40 for only a little more than that, and I have definitely gotten my moneys worth out of it) that might be put to better use elsewhere. Since the lens is 3rd party, there is always the risk of problems (especially with focusing) which I would prefer to not have to deal with (but I would if I had to). With this lens, my night sport photos could be improved greatly (I know the photographer is the most important part of a good photo, but when shooting sports in very dark conditions, my gear has become the limiting factor), but the camera would also help with that, and the camera would help more when shooting in daylight, where I would stop the lens down anyway.
Downsides of the 70d compared to the 70-200:
Since the tamron is a lens, and not a camera body, it will serve me more long term (as is evident when looking at how many years my dad's tamron lenses outlived his canon body...). Another note about long term use to keep in mind with my decision, I will be going to college in just over a year, and I am hoping to shoot the football games and other sports for the school newspaper, magazine, and whatnot.
Now I realize that these are two very different things I am comparing, but I am looking for help with deciding which would help me make better photos the best (as a reference I shoot mostly landscapes, sports, performances, and long exposures). Also, I will (hopefully) have enough money in a year for the item that I due not choose, since I will be graduating then. (but in that case, if I get the lens, then Canon will most likely have released another camera that I could get... ahhh so many options!)), as well as in the long run. Any advice/experience is greatly appreciated. Sorry for using so many parenthesis... Thanks!!
Also, since this is about both a camera and a lens, I put it in the lens section due to the larger amount of traffic.