Canon 600d vs Sony PD170 for video production
It's a little bit subjective. DSLR footage, straight off the camera, is very crisp and clean. Whereas a PD170 has a bit more of a 'video' look. So first off you'd have to decide what kind of look you wanted to go for. 

In most cases you would choose to shoot on a DSLR, simply because the image is more visually appealing. 

Pros of DSLR:


better looking footage (subjective, although a common view)
can attach a variety of lenses (i.e. fish-eye)
smaller body, more mobility
no need to import footage off a tape, just copy and paste off SD card onto computer
it's cheaper


Pros of PD170:


don't have to worry about the camera overheating (can shoot as long as the tape and/or batter allow. DSLRs tend to overheat after 10minutes of straight shooting)
larger body. Easier to do handheld with just the body alone
can plug in a microphone directly into the camera. This avoids having to use a clapper before each take and avoids the need of syncing audio and video


For me, those are the main points. If you're looking to make a film cheaply, DSLR is the way to go. But don't forget about sound; good sound is integral to a film.