Grinding Advance means baneblades are inferior to their points in Leman Russes. The shadowsword comes out better because of the 3d3 s16 ap-5 2d6 damage gun. If you want efficiency, only the Shadowsword is worth it, but that's why we suggest magnetizing it as per the tutorial posted, so you can enjoy all of them at your leisure.
On the Baneblade (and variants - which I will refer to collectively as the 'Baneblade' from here on) vs. equal number of Leman Russes note, the Baneblade hulls have a notable advantage when melee is considered - the Overwatch from multiple Leman Russ tanks can be reduced by charging one at a time; the Baneblade actually has a chance to kill something in the Fight phase; and most importantly, a Baneblade's shooting can't be shut down by being within 1" of an enemy, unlike the Leman Russ.
Additionally, the Baneblade gets far more mileage out of Stratagems. Crush Them is actually useful on our Super-Heavies, and Vengeance for Cadia and Defensive Gunners have more of an impact when applied to a Baneblade rather than a Leman Russ.
All in all, I think both options have their strengths, and while the Baneblade variants might lose in firepower when compared to equal points of Leman Russes, they do have their advantages, too.
(and I agree with the Shadowsword being the best out of the Baneblade hulls - a pity, as the standard Baneblade looks so cool)