Well, if you have an XD 40 you can buy a .357 Sig barrel for it on midwayusa.com for about $185 and then a few .357 Sig mags for it and now you've got a completely different caliber gun for about $200 or so. So the XD can be two different guns for a fraction of the cost. That being the case I would go with the Taurus 24/7 because I like the premise that its built on. It seems like a very well put-together gun and when I move to Arizona I may just buy one myself. However if we were to compare both companies, Springfield and Taurus, Springfield puts a lot more work and effort into the engineering and construction of their firearms whereas Taurus doesn't. Springfield (the original armory) had U.S. war contracts for weapons. The government isn't going to do that with just any manufacturer. The M1 Garand made the Americans a force to be reckoned with in WWII as it was far superior to the Lee Enfield due to its stripper clip loading instead of bolt action firing which was far more condusive on the battlefield, and its accuracy was phenomonal. But I digress.
I'm going off on a tangent. But to answer your question, this particular time I would say go for the 24/7, you've already got an XD dude. Switch it up a little bit. Its not fun going to the range with a bunch of the same guns, just in different calibers. What makes it fun is different trigger pulls, different weights, different feels, different recoils, etc.
