Hello again Jinay
Firstly, I agree with Wolfsong and I also regularly check out his and KPR's pics - thumbs up there.
I do not post photo's - one day I will just right now I can't fit it in however Wolfsong and KPR regularly upload their pics so any advice they give you is backed up by their pics so if anything I say contradicts them (I will try not to) it's probably best to listen to them
I have the Sigma as mentioned above and it is far from perfect but I like it however, I am hoping to purchase a lens of at least 500mm as Wolfsong says 300mm is not always long enough.
If my memory serves me correctly the sigma and tamron are roughly similar in autofocus and I chose the sigma as the macro capability appeared to be better than the Tamron as well as the shorter end of the zoom but the Tamron wins at the 300mm end so in my humble opinion there are three good reasons to go for the Tamron.
1. It's cheaper
2. It will be better at 300mm which should be more suited to your needs
3. The money you save could be saved towards a longer lens you will almost certainly want at a later date
In terms or autofocus I use the Pentax K10d - many say that the autofocus is slower than rivals, they are probably right but it is quick enough for me.
My sigma 70-300 is faster and more precise that my 18-55 Pentax kit lens (a bit surprising I suppose) but maybe not as quick as my Sigma 50mm ex dg macro but there is not a lot in it.
One thing I have noticed is whilst pointing the lens at birds, squirrels etc the lens/autofocus will change in an instant should something else cross the selected af point such as another bird, sometimes insects (bees are not as much of a problem as butterflies (kinda obvious I suppose), branches moving in the wind or even a falling leaf this can ruin the shot but shows how quick the focus actually is - not always a good thing as the focus sometimes locks on to the other subject momentarily and then flicks back to the original target other times it just gets momentarily confused. I am yet to use a more expensive lens so cannot give a comparison here (help - Wolfsong/KPR maybe)
I have plent of shots of moving animals, birds etc but squirrels seem to hide from me - I will track them down
It takes a bit of practice to track moving objects but it can be done I really like the Sigma and should I not splash out on something such as the Sigma 150- 500 (The Tamron 200-500 is not available in a Pentax mount, in the UK at least) then I may look at obtaining a used Tamrom 70-300 for use with for shooting birds using the 300mm end.
If you like the Tamron as much as I do the Sigma then your money will have been well spent - that is of course my opinion and that's all.