I think they are such different bags to compare. I think the coffer is too tailored for my taste, I'd take a bal over that any day. course if you ask in the Mui Mui forum they'll say just the opposite! lol!
I've got a black lambskin coffer (got it in 2007) and i don't baby it at ALL and the leather is as buttery and as smooshy as ever. it's my go-to bag, it fits everything and yet it is not so wide so that things fall over inside it. I also love that it had a shoulder strap (very comfy) and that you can use the longer cross-body stap. It is less bulky than the work, and I find that the black with gold hardware is delicious -- I get stopped and complimented on the coffer all the time!
finally, I don't find the coffer heavy at all -- unless i stuff it with my various things. even then, the thick smooshy braided strap is comfy on my shoulder and you would be surprised as to how much you can fit in there.
i love me some Bal, but the Coffer is my First Love (and my classic love)
I have both and surprisingly I use the coffer much more often than the work. I have found that it's easier to carry the coffer cross body whenever I go shopping. I like the outside pockets on the coffer where I can put my keys in one and my iphone in another whereas I have to really dig and rifle through the work to find either one of them. For me, coffer just seems to be a more practical bag.
Nevertheless both are gorgeous and different in its own way. GL and please let us know what you decide.