bigger woofer always better?

Yes I would since the M-L is from a highly respected high end speaker manufacturer and the BA is from a run of the mill mid-fi company. Also it's not really the size of the woofer as much as how it's implemented and the quality of the driver. A high quality 10" woofer is going to beat a crappy 12" woofer every time. I don't mean to sound elitist or anything, it;s just that those two companies aren't really in the same league. Happy listening!

"Also it's not really the size of the woofer as much as how it's implemented and the quality of the driver. A high quality 10" woofer is going to beat a crappy 12" woofer every time."
-Jond

Well stated, in my opinion. Also, you've probably already answered your own question when you said this:

"...I was very impressed with the Martin Logan. It delivered a tigher bass and don´t know why it even sounds louder and stronger..."

If the you heard was that dramatic, then it's probably real. There's no reason not to trust your own ears. I'm with Jond. I'd go for it, if it's financially feasible.
-Bill