I've owned them both, and they both have their pros and cons, IMO. My EMP was in 9mm, and the Defenders I've owned were in 9mm and .45 ACP.
The EMP was about $200 higher than the Defender in the gun shops around where I lived. The EMP is a somewhat smaller gun, which may make it easier to carry (I didn't carry either one.) The EMP isn't a "traditional" 1911, and doesn't accept many standard 1911 parts. Both of them seem to hold their value, although Colt has many more fans. Both shoot very well, IMO, and mine were reliable.
Springfield has excellent service (I had experience with them on a different pistol) and they are very fast. Colt's service varies from slow to very slow...and they sometimes get focused on large contracts (primarily military and police) and individual guns can get pushed to the back burner. I've owned a number of Colt 1911s, from full size, Commander, and Defender, and I only had a problem with one (and it was pretty minor, but took a LONG time to get resolved.) Colt makes a beautiful gun, IMO, but then the EMP is a little jewel in its own right.
I don't think you could really go wrong with either one, depending on what you want. If you want a great little carry gun, the EMP will certainly fill the bill. The Defender will as well, and also being a Colt, has a rich American tradition. The Defender does have one advantage that the EMP doesn't (unless they have started making one lately) and that is it is available in .45 ACP.