I'm not very familiar with the Colt Defender, but 3" 1911s aren't thought very highly of around here.
With good reason... there are some pretty significant reliability issues that have surfaced.
I know for sure that springfield and kimber have had their share of problems, with 3" 1911s, and I experienced problems with my EMP40 at first. Of course, there are also reports of issues with full size pistols from those companies, so it could be due to a QC issue.
My emp runs 100% after sending it back to springfield, and it doesn't seem to be picky with ammunition. There are also plenty of 3" 1911s out there that run fine, with no problems, it's hit or miss.
I trust mine, and I'm not saying you shouldn't get one, but it is something you should consider before purchasing one.
What he said. A 1911 with a 4" or 4.25" (commander) barrel and Officer size frame will conceal just as easily, the only difference is an extra inch in your pants (and who doesn't want an extra inch in their pants?!). It will be inherently more reliable and you'll also gain some velocity and increased sight radius.