Well it all depends on your sound and your needs. But I'll try to shed some light on the things I know.
If you want pure rock, tube powered fun, go with the Big Block. This is THE rock Boogie to compete with a Recto. Not the amp for a bass virtuoso.
If you want more options go with M-Pulse 600, it's a cleaner, more articulate sound but has tons of feature that make it really versatile. So more complicated techniques come out clean.
If the M-Pulse is too much for you, the Scout is a scaled down option that has a little less headroom, giving it a more soft, vintage feel. Lots of older guys love this one because it sounds old and it's light weight
If you'd like a mix of the of the M-Pulse and Big Block, go the M6 or M9 Carbine. Flexible sounds,lots of features but can go from clean to crunchy.
Those are the current models. I guess you could choose your cabs to what your doing. I currently play the M-Pulse Venture (a 2x10 combo) but I think I'll be switching to the M9 within the next couple of years.