Well the point is that you wouldnt just learn a language, you would want to learn a language that you can actually practice and actually use.
For example - are you likely to buy and use Motorolla HC11 chips to do anything? Probably not, so learning it may not help much. It is true that many assembly languages are similar but also every is different.
I suggest that you learn somehting like Intell Assembly. That was you can write programs and test it out on your computer. Intell assembly is very powerfull and you have a ton of registers to use, ans alot of commands to use. You might htink having alot makes it more complicated but it is actually easier.
PIC assembly for example only has a few instructions and 1 register, so it can be complicated to do simple things with such limited resources.
I myself did not learn Intel Assembly as that was a computer science cource I neevr got arround to taking - but I'm sure it wouldnt be that hard to find help or even tutorials online.
My second choice would be to learn pic assembly, because I friggen love PIC chips. I feel like I can build anything with a PIC - and you can even get free samples. Although there would be some hardware and circuitry building necessary with those so its up to you, but I think Intell Assembly is a more resonable choice.