The Tamron is a great place to start. But if you get proficient using it, eventually it won't be sharp enough. I'd say buy it, see how much you like using it, but save up for the 55-300. I had the Sigma 70-300 not the Tamron, and I came to a pretty good understanding of how much I enjoy useing long lenses. But as soon as I started looking at producing pro quality images, I wanted something better. That being said, some of my favourite images were taken with it, I learned a lot using it, and not every image needs to be razor sharp to be effective. You can do a lot with such a lens. And if you are a guy like me, the macro function was a big part of my enjoyment of the lens. I seriously wish there was a pro quality lens with the same functionality. I love the quality of my telephotos and macro lenses, but I have to carry two lenses instead of one.
My advice would be start with a cheap Sigma or Tamron. Then shoot with it until your technique demands more resolving power. It was about 5 years before I became unhappy with my Sigma. The problem with starting with an expensive lens, is, you may never develop the technique and experience to exploit it. 70-300 lenses will get you going at a lot less cost, and let you get your feet wet without gambling on more expensive gear, that you think you might like, but which in the end really doesn't suit your style.
Last edited by normhead; 07-19-2017 at 11:49 AM.