I don't have a lot of experience with Stop Motion Pro, at least not the more recent versions of it. But, I prefer Dragonframe, partly because I just like the GUI design better and primarily because the motion control and arduino integration is incredibly easy and well designed. Plus you get a nice USB keypad rather than just keypad stickers. Depending on whether or not you'll ever use the Arduino control of either program though you may want to jump for SMP as it's a fair bit cheaper than Dragonframe but maintains much of the same essential functionality. All in all both programs more or less have the same features, the only differences being how they're laid out and the control within the software.
Both companies offer free trial downloads, so you may want to try the trials of both and see which one feels better to you.
I haven't used Eclipse, because my old PC finally died. Until SMP comes up with a native Mac OSX version, I'm using Dragonframe on the iMac that replaced the PC in the studio. I have used both SMP and Dragonframe quite lot and I'm happy with either of them.
For shots where I need to take each frame twice, like stereo 3d with a left and right frame, of frontlight-backlight, I prefer Stop Motion Pro. You can name your 2 frames, like Leftview and Rightview, and after you take the first one a window pops up in the middle telling you that you've taken Leftview and that Rightview is still to be taken. Can't miss it. In DF, there is a thin strip across the top of the screen that changes from grey to dull green or something, but it is not something you would even notice. And the exposures are called 1 and 2, in tiny tiny print on my big monitor, and it was very easy to lose track of which one was taken. But once you know where to look, it's not a problem anymore. I stuffed up a couple of frontlight-backlight shots before I worked out how to know which was which, then I knew so it was ok after that. Actually there are a few things I found harder to find and figure out with DF, but once you know you forget about those things and it all works fine.
I don't use the keypad that came with DF. I always want to be up close to the monitor when I take the shot, so I may as well use my ordinary keyboard and mouse. I use the onscreen keypad and click with the mouse to take the shot. I don't have room for an additional keypad.
I don't use any of the Arduino stuff, can't afford motion control or lighting control, so that was not a factor for me.
For dialog, DF seemed to work better at loading the wav file of the speech in, and letting you see and hear the sounds as you are animating, than the older version of SMP. It may have just been a bit weird on my 15 year old Pentium 4. But I think audio in Eclipse is improved. I no longer have a working PC to try it out on though. I had been using a Mac for all my post production work for some time anyway, and had put DF on it to drag to the studio as a second framegrabber on a couple of occasions.
Best option, like Ethan said, is to try the free demos and make sure they work on your PC, with your camera, and with your brain. I found no difference between the two when it comes to working with my Canon 40d or 7d, and no difference in the images saved on the computer.
I like to use the arrow keys to click forward and back to the last frame taken, and whenever I updated SMP I had to go in and change the keyboard shortcuts so that the arrows were the right ones. I think a couple of letter keys were the default, not as intuitive, but easy to change. Once done, I forget I even did that until next time I upgrade. They may even have changed that in Eclipse.
I've tried SMP and Dragonframe on my PC and they're both excellent programs. I ended up picking Dragonframe to buy.
I'm a complete novice and don't do anything fancy with them, just very straight forward animate and export the jpgs, but so far I've really been happy with the program.
If you're working in the UK every company I've worked for and looked into working for use Dragonframe so might be best to familiarize yourself with Dragon. I use it all the time and its good stuff