I got my XD as I had been wanting a .45 for awhile, and finally decided it was time. I've had a Glock 19 as my go-to gun for about 15 years now so I was initially leaning towards a Glock 21SF. But then I heard about the XDs and was intrigued. I went to the range and fired some, and I was impressed. As much as the Glock felt initially familiar, I had to admit that despite years of shooting my Glock, the 1911 style grip angle of the XD felt more natural to me (who knew?). The trigger felt smoother, it had a bit less felt recoil, and I shot better with it. I was sold.
As to why I chose the Tactical model? I already have a compact gun in my G19, and wanted a full size .45 model. It's my first .45 and I figured a full size model would be easier to shoot and adapt to, and so far my XD has done well in that regard. I like the way it feels and balances in my hand, with or without a full clip.
In fact, I like my XD so much I'm now waiting for the XDM 9mm model to come out so I can buy one of those as well. My trusty Glock will get "retired" from nightstand etc duty and the XDM will take over, with it's big brother the .45 when I want a bigger gun.