Alright, so this is a little complicated.
If I'm not interested in a TAS too much (I am not familiar with the game but the TAS sounds promising enough that I want to watch it anyway), I usually open the YouTube page and watch from there (highest available quality). This used to not be a real option before 60 FPS on YouTube, but since that got introduced, I'm much more likely to give a shot to a TAS of a game that's new to me. It's very convenient because I'm one click and zero delay away from watching, which is minimal time loss in case I end up not interested.
If I'm interested in a TAS, I usually go for the MKV. I'd really like to always watch MKV since it offers accurate framerate and color (no chroma subsampling and 10-bit), however sometimes I have to fall back to YouTube because:
- the YouTube encode may offer additional editing not available in the MKV (example:
[3530] DS Mario & Luigi: Partners in Time by Migu in 3:21:09.92, although Spikestuff posted MKVs with editing in the forum thread for that one);
- the YouTube encode may offer additional HUDs not available in the MKV (example:
[3497] PSX Crash Bandicoot: Warped "item glitch, gate clip" by pirohiko in 05:40.77, this one has HUDs in the author's encode, which is usually the case, so I end up watching that, even if the quality isn't the highest);
- the YouTube encode may offer commentary (example:
[2711] PSX Spyro: Year of the Dragon "117%" by Nitrofski in 2:27:54.15, commentary in the author's encode).
Sometimes if the quality of the YouTube video with commentary is bad like in
[3592] PSX Crash Bandicoot: Warped "105%" by The8bitbeast in 1:54:18.52 I may even open the MKV and the commentary video side by side to watch the MKV with the sound coming from the commentray video (yes I know I can ffmpeg the two together but it's easier to just sync two video players manually than having to deal with audio discrepancies).
That said, I wish the MKV encodes used a lower CRF since video compression artifacts are frequently easily noticeable, especially on encodes of lower resolution consoles.