[Papa_Joe]

Get some more insight from the direct comparison through pentaxforums.
Fast Sports Zoom Lenses for Pentax Review - 70-200mm Sigma & Tamron | PentaxForums.com Reviews

I have the tamron since four weeks and the IQ is outstandig good. One of my best three lenses (beside the Sigmas 35/1.4 and 70/2.8).
The screw drive is quite fast. It is not silent, but I would not call it noisy. If you need a silent lens you are wrong with the Tamron.
Opposit to the test above, I find the Tamron quite good to hold if the tripod colar is removed, which is a thing of half a minute.
Although the built quality is very good, the Tamron feels a bit plastic. When firing the shutter the sound always reminds me of a yogurt cup. So, if you like a sturdy lens, the Tamron might disappoint you.
I am personally very happy with the Tamron. Makes me smile when I use it and even more when I look at the results.

For the K3 I would also think about the Pentax DA 60-250 / 4, if you haven't allready.

[normhead]

Get some more insight from the direct comparison through pentaxforums.
Fast Sports Zoom Lenses for Pentax Review - 70-200mm Sigma & Tamron | PentaxForums.com Reviews

I have the tamron since four weeks and the IQ is outstandig good. One of my best three lenses (beside the Sigmas 35/1.4 and 70/2.8).
The screw drive is quite fast. It is not silent, but I would not call it noisy. If you need a silent lens you are wrong with the Tamron.
Opposit to the test above, I find the Tamron quite good to hold if the tripod colar is removed, which is a thing of half a minute.
Although the built quality is very good, the Tamron feels a bit plastic. When firing the shutter the sound always reminds me of a yogurt cup. So, if you like a sturdy lens, the Tamron might disappoint you.
I am personally very happy with the Tamron. Makes me smile when I use it and even more when I look at the results.

For the K3 I would also think about the Pentax DA 60-250 / 4, if you haven't allready.

For sports, low light and action shooters ƒ4 compared to ƒ2.8 and the slower AF on the 60-250 tend to be the defining metrics.
As a landscape shooter with occasional wildlife I find the 60-250 adequate, that's it's niche.

[gatorguy]

Get some more insight from the direct comparison through pentaxforums.
Fast Sports Zoom Lenses for Pentax Review - 70-200mm Sigma & Tamron | PentaxForums.com Reviews

I have the tamron since four weeks and the IQ is outstandig good. One of my best three lenses (beside the Sigmas 35/1.4 and 70/2.8).
The screw drive is quite fast. It is not silent, but I would not call it noisy. If you need a silent lens you are wrong with the Tamron.
Opposit to the test above, I find the Tamron quite good to hold if the tripod colar is removed, which is a thing of half a minute.
Although the built quality is very good, the Tamron feels a bit plastic. When firing the shutter the sound always reminds me of a yogurt cup. So, if you like a sturdy lens, the Tamron might disappoint you.
I am personally very happy with the Tamron. Makes me smile when I use it and even more when I look at the results.

For the K3 I would also think about the Pentax DA 60-250 / 4, if you haven't allready.

I hadn't mentioned it yet because I'm waiting on one of them but as of this weekend I'll have BOTH the Sigma and Tamron 70-200 2.8 assuming the delivery estimate is accurate.

I'll be keeping one and selling the other depending on which serves my personal uses better. FWIW the screwdrive sound has only rarely been an issue and Tamron reviews have been very positive so at the moment I'll still leaning Tamron but once I have both I may change my mind.