I started out with the aluminum Investigator, which I got at Blade 2011, and I loved it. Then I ran up on a couple SS Investigators, which I absolutely loved, even more than the aluminum, because of the added weight. I have medium sized hands, and I think it is perfectly sized for an everyday carry writing instrument.
I love the SS investigators so much, that I finally decided to pull the trigger on a Titanium Investigator, and its on the way now. I can't wait for it to arrive. I held the Extreme Duty at the show, and it seemed to big to carry on a daily basis, as I already carry tons of stuff in my pockets, so the investigator, fitting my hand as well as it does, was the obvious choice for me, and I can't say enough great things about it.
I guess if you are looking for another weapon to pack around, the extreme duty pen or modular kubaton is the way to go, but if you're seriously just looking for a great pen to carry and use on a daily basis, and you don't have huge hands, then the investigator is the way to go, in my opinion.