The trade-off is that 25p will give sharper video during low motion, while 50i will give smoother motion with less jitter. 50p gives the best of both worlds.

If it's low light 50i will give 6dB less noise than 25p.

Bob.

Thanks for the replies guys. Sounds like 25p in good light then, and 50i in low light? Does Vegas handle that mixture OK? If I've got all 3 on the TL, what would be the best project settings? Best render settings? I've got a couple of weeks to experiment.

The most important setting, I guess you already know, is Deinterlace Method : Interpolate.

Other than that, what is your final format and delivery for this project?

+1 set

I also think the most important question is delivery. If its DVD I would go with 50i all the way.

With 50i, shutter speed cannot be lower than 1/50,
with 25p you can go to 1/25 if needed.
So better in lowlight. Not?

@relaxvideo

with 25p and 1/25 shutter you can only shoot from a very stable tripod and have zero motion, nothing else. As I learned in this forum, your shutter is should be always 2x the the frame rate which would be 1/50 for 25p and 1/48 for 24p. Even at 30p I shoot 1/60 minimum, sometimes 1/90 to 1/120 for higher motion.

agree with Oldsmoke, this is a basic of cinema settings.., in which in film cameras, shutter angle 180 degrees. ( http://en.wikipedia.org/wiki/Rotary_disc_shutter )

The delivery will be BD and DVD...call me mister awkward. :-) Looking like 50i then I'd say.

In that case I would rather set all cameras the same, 50i would be my choice.

Oldsmoke: yes, i also know this rule.
But then
25fps: min 1/50 shutter
50i: min 1/100 shutter?

It depends. If you record very fast motion then yes.