I have found a gig, but the only problem is, I'll be working on a L visa.

You use 'on the other hand' when you're providing two pieces of information about one thing. In maths, it's 1-2 correspondence from set A to set B. It's not this situation in this case. Your post is 1-1 correspondence from set A to set B.
Set A is the two distinct employers. Set B is the two distinct visa types.
Employer X requires you to work on an L visa
Employer KC 'guarantees' you a Z visa.

Instead of 'on the other hand', you should have typed 'in contrast' or 'by contrast' .

If it were me, I'd possibly accept the job offer from employer X. But my final decision would depend mainly on the job's location - boondocks or big city, the former preferred; public gig or private gig, the former preferred, training centres, certainly not.
But of course, you can turn down both job offers and keep looking!