Deffinatly infrared, I use both sometimes but I keep the flash off on the one that has it because I have consecutive pics of it actually chasing deer away at night.
To me it comes down to personal preferences as I have seen deer spook from the flash just as often as I have from the IR lights. I have a few of each. The Flash cameras take great night pics and the IR for night videos.
What Pat says is very true. I have even had them stand and stare at the cam when there's no flash of any kind. IR cams are better with battery life but almost any movement in a night pic will result in the picture being blurred. There are some cams that are worse than others in this area but they all seem to do it. I would advise you to stay away from the really cheap cameras. The problem with them is the quality on the low priced cameras is hit and miss. You might get a good one or you might not. I personally think you need to be in the neighborhood of $150 to get a solid unit. Blessings.......Pastorjim
If you put the cam on something that the deer want or need, such as food, food plots, water, mineral site or scrape, I'd use a flash camera. They'll pose all day or night for the best pics. Otherwise, if it is placed just on a trail, it will spook them more and sometimes cause them to skirt around the cam.
Moultrie m-80 IR for me. Great battery life, clear pics day or night, reasonably priced, and it is extremely user friendly when initially setting up the camera. Here are some sample pics from mine. Note that these are pics of my laptop screen with my iPhone, so if they appear blurry I apologize, from where I'm sitting they're quite clear :-)
I have both and I'll be buying some more flash cameras this off season. I love the IR cameras on video mode over scrapes and trails but I hated them on food plots at night because the IR doesn't have the range of flash cameras. With video mode deer do react to the IR as much as any flash camera I've had and the blurry images when moving is quite annoying, its preference and use you need to take into consideration.