Sigma 70-200/2.8 vs Tamron 35-150/2.8-4

[bravo7490]

Hi,
Totally new to this forum and digital photography.
I have a Canon 70D with a Sigma 17-50/2.8. I'm interested in shooting people, and possibly a little street photography. I shot a model in a class recently and realized I needed a longer lens.
My question: Should I sell the Sigma and get the new Tamron 35-150, so I have everything (for now) I need in one lens, or should I buy the Sigma 70-200/2.8, or possibly the Canon 70-200/4, and have two lenses, my present sigma of 17-50 plus a 70-200?
Thanks,
Dennis

 

[troutfisher]

If you sell the 17-50 you will loose the short ( wide ) end and will probably end up buying something along the 10-** line, plus the Tamron is f2.8 at the short end and f4 at 150mm.
Get the 70-200 it depends if you want f2.8 or f4 one point to bear in mind is the canon is half the weight of the sigma.