I want to do youtube covers.
help me pls.
the reason I want to use Multi fx because I can plug them straight to the computer and get awesome sound
so which one should I get?
Boss GT10/GT8 = tons of high quality effects, good tone, can handle extreme metal.

Vox Tonelab = less effects, lower effect quality, great tone, can handle rock and classic metal but not extreme metal.
For amp modeling, unquestionably the Tonelab.
Dear God, do you actually answer prayers?

Yes, but only in a way indistinguishable from random luck or the result of your own efforts.
I have the boss and it's great for recording

you can use the USB cable or the headphone out
and you can use 2 different tones is stereo
Tonelab's great except for high gain. If you want to play metal a lot and record directly from the board, it's probably not for you. It's hard to beat for low gain sounds though.

And if you can afford to, get a Digitech Eleven. Awesome, just awesome.
I found the Tonelab to be just okay, but had the GT 8 for a month as I rented it from the music store (I intend to purchase one soon) and I found it did everything from cleans to high gain very well. Didn't get a chance to record with it as I had latency issues direct out, and didn't have the USB to record with, but through the effects return of my Peavey it kicked serious ass.
Never played the other two so I can't compare but here's what I don't like about the Tonelab...

Can only use on of the effects on each dial. i.e. one reverb, one delay, one modulation/filter.
Can't do the high gain as mentioned... but a pedal in the "insert" loop solved that problem.
Like I said I haven't played the others to compare, but I felt it was a bit limited in the effects somehow.
My expression pedal broke and doesn't hold itself up anymore.

It sounds great and the amp modeling is good as well though.
I have a huge fear if rays.