For MM I can't recommend BB1 anymore as it's already starting to wither, and tbh I never liked it for leagues anyway, fumbbl being my league BB of choice because the much more comprehensive house rules you can choose from.
So basically for open MM play BB2 manages to fit the bill, even with the missing teams. Really it just needs Undead, Goblins, Pro Elves, Vampires, and CDorfs to really fit the bill for all the most commonly played races.
It's also far, far more new player friendly, with showing the percentages of actions, what block dice will do if you hover over them, the skill icons both being worse and better (worse to start, better when you're used to them as it lets you view the whole team at once in the team management screens), the lack of hover names is shit though, so we'll see if that's fixed.
The new rules are also IMHO an improvement in most cases, especially the (unanimously agreed on by the BBRC) treasury bank rule that was supposed to be in LRB6 before Jervis threw a shitfit and used his veto power to put his pet rule in instead. Aging is back from LRB4, except now it's only the retirement part, not the horrible constant stat decay, and the new stadium improvements, while I can't find much previous stuff on it like the other changes, do add a nice dynamic, especially as upgrades affect teams equally (for instance making any failed GFI roll add +1 to armor break for the failure, or both teams getting a free bribe). The wizard one is fairly problematic as a free wizard for both sides favors AGI teams by quite alot, but thankfully not many people seem to take it out of irrational fear.
It should be noted that for private leagues aging can be disabled, and stadium upgrades can easily be house rule enforced. The bank rule however is not optional, but is frankly a better way of handling it than the old petty cash rule.
Basically the old petty cash rule from LRB6 was that any cash added added to opponents petty cash as well, and couldn't stack with petty cash. This caused two problems. 1) If you were the top team, you never ever had a reason to buy inducements. 2) If you were the bottom team and you were a bit short, you couldn't do anything about it.
The new rule doesn't do cash adding, but also makes any cash over 150,000 (Considered to be the usual nest egg you want to keep) count for tv. So lower value teams can spend the extra 10k if they reall need it, while rich teams (almost always bashy guys who dont take as many casulties because bash) are both discouraged from hoarding gold like a kleptomaniac dragon (I have seen max fed Chaos teams with over 10 million gold in bb1 before), and have a reason to actually spend it.
The new race, Brettonians, also aren't a Cyanide invention, and are isntead a roster that have been around for awhile in various fan communities.
Lastly, there have been hints by Cyanide we might get a Slaan team this time around. Slaan, while a BBRC approved team, was not in BBCE because GW never sold minis for them, same as Chaos Pact.