Canon T4i: What is the best quality/best way to transfer HD video to MacBook Pro...

I'm not sure exactly what kind of information you're looking for.

For getting your files to the computer, there is no "best" way. Just use the usb cable or a card reader if you have one.

As for getting them on youtube, are you editing them first or do you just want the clips up there as is? Because if it's the latter, then just upload the clips directly to youtube. They're already h264 and you're not getting any higher quality than what's ripped straight from the camera.

This really comes down to a workflow preference. I still use FCP7 and tend to use log and transfer. That said, I also use mpeg streamclip for converting some video to ProRes.

Final Cut Pro HD Express may present some challenges for you and mpeg streamclip may be your only option there. I'm not sure if ProRes was included with Express.

Premiere over Premeire Pro may also present some challenges. What version are you using?

You might not need MPEG Streamclip to convert the files for editing in FCE, if your camera already records in quicktime or h264. I used FCE for a while until I got FCP X. My camera was a Nikon D90 and I had to use MPEG Streamclip to edit natively in FCE since that camera recorded video in motion jpeg, if i remember correctly.

FCE won't output your files in 24 FPS. The closest thing was 25 FPS, so that is what I used to export video from FCE. FCE will work using 24 FPS media, just not able to output final edit in 24 FPS, if that makes sense. So, your 1080P/24 FPS is fine, except for the exporting part.

Anyway, I used Apple Intermediate Codec when converting the D90 files with MPEG Streamclip for editing in FCE. And from what i can tell with my naked eye, i couldn't tell the difference between the original source file and the converted file.

hope this helps.