Which is the better DSLR: The Canon T3i, the Nikon 5100, or the Sony A65?

so why exactly do you want to use a DSLR for video purposes? for the same price, you can get a nice video camera that will do video much better than any DSLR such as this: http://www.bhphotovideo.com/c/product/749189-REG/Canon_5127B001_VIXIA_HF_S30_Flash.html

nikon d5100, compare them at snapsort.com/compare DO NOT BUY CANON, their mirror unit are made out of cheap plastic the mirror broke in 2 days!!!!

Shooting video on a DSLR-type camera then Sony's SLT-A65 is the runaway winner. It's the only one you've listed that can continuously focus while shooting video (without fuss, though this may not be such as great feature as you currently believe). Shooting 1080p @ 50/60 fps (region dependant) in movie mode and hitting your 10fps @ 24mp in still mode. You can push the sensitivity higher on the A65 than on the Nikon or Canon, though at high ISO it will get noisy (you'll notice noise more in still images than you will in video). A point on AF while shooting video, it does mean you need an external microphone, otherwise any mic located in the body picks up the noise of the body/lens focusing mechanism. Sony's SLT-A65 delivers better video performance than even Canon's 60D, it's closest competitor is Nikon's D7000 and Sony's own SLT-A77. There is an advantage to the the Nikon D7000 and Sony SLT-A77 as they use the body as a heat sink to keep the sensor cool meaning that you can shoot longer video sequences before they shut down. Be warned that shooting video on a DSLR may mean the files are "loss-less" ie not very compressed and so the initial output files while great quality may be massive!

.I won't cover every single thing, but here's a few thoughts. All great cameras, no doubt. But none of them are going to meet your needs. The only one that might is the new Canon 5D mark III, but even that does not appear to shoot 60p video. http://www.dpreview.com/news/2012/03/02/Canon-EOS-5D-Mark-III-preview The Canon bodies get a better rep for video, but it's been usability issues, not really for having better image quality. Also, I think Canon was the first to get full 1080p in a dSLR. The Nikon's, overall are better rated for cleaner images at high ISO using Sony's best image sensors for the money. Sony has lagged behind in low light high ISO because of the translucent mirror or using older gen sensors in their entry level bodies. Robbing the sensor of light means noisier images bringing them to Canon high ISO numbers. I know more about the Sony because I shoot Sony Alpha, so let me cover that. The A65 does not have an OLED display, it has a OLED viewfinder, the LCD screen is standard stuff, good but nothing new. It does have a fantastic swivel screen. While the A65 does do 60p, it's not the cleanest image sensor for low light work. It has too many pixels (24MP) packed into the sensor, and it's pretty bad by ISO 1600. Also, I know the A77 is capped at ISO 1600 when shooting video if I remember correctly so the A65 should be the same. Even with its issues, for heavy video shooting, I'd take the Sony A65 over the others. For shooting mostly stills, I'd go with the Nikon. The image sensor in the 60D, or the 7D is no better than those found in the cheaper Canon's (according to DXOmark) so only go for the higher end Canon bodies for the features it has over the others. Glass isn't an issue for any brand. The Sony gets a bad rap about glass, but the truth is, the most common lenses you find people use with Nikon or Canon you can find in the A-mount for Sony. You can use Sony branded lenses, Tamron and Sigma A mount glass, Zeiss AF lenes, and all the AF Minlota lenses work too, and there are millions of them. The Sony is the only one that can shoot video with fast auto focus if you want AF. Canon and Nikon use slow contrast focus, and don't offer fast AF with video at any price. One final thing, your lens choice is fine if the light is good, but in low light it's no good, paired with the A65 in low light or at night, not a good combo. Large aperture zooms are always expensive. Your only option for a large aperture for low light without spending big money would be a 50mm f/1.8 prime. In Canon or Sony, no issue, be careful with Nikon. The entry level Nikon's do not have AF motors, and not all lenses have motors like the most common 50mm f/1.8 Nikon lens. Make sure any Nikon lens you buy has a motor. If you step up to a D7000, it has a the AF motor.

If your primary purpose is video, the Sony a65 is your best bet out of those. The translucent non-moving mirror allows you to use the viewfinder during video mode and it also allows for continuous autofocus. Using this camera in video mode is very much like using a regular video camera except that it does cut off and you have to re-start the video, like with all DSLRs. It also has an external mic input and flip out screen (well all three of them have that) which is helpful for video.