Light Bracket — LCT-1E
Not many options here. COM-2D may be attractive, but with the SSRM2's being almost useless, your best bet is the Locust. Among them, I suggest the 1E without even hesitating. With 6 arm-mounted energy hardpoints, this is the hardest hitting Locust without the annoying torso-mounted hardpoints. At only 1 million C-Bills, this is a no-brainer. Just don't build it for Small Lasers as the quirk suggest, they're horrible. SPL's ftw!
Medium Bracket — CDA-2B/3C
Lots of good 'Mechs on sale here. You should obviously first look at completing your Hunchback collection (all of them are great with the quirks). Otherwise, check out the CDA-2B and 3C. Especially the 2B is a monster with MPLs at the moment and will absolutely demolish anything foolish enough to go after it at close ranges. 3C is also a honorable mention with its ridiculous ERPPC quirks. Especially the range and speed bonuses are really nice. It's not a killer like the 2B, but it's a great harasser at long range. Dropping to Alpine is like going to heaven with this thing with 1000+ ERPPC optimal range. A true harasser 'Mech.
Heavy Bracket — ON1-K
If you ignore the Jagermechs here, the ON1-K is the only option that screams "BUY ME!" even though it's only one variant. For those unfamiliar with the Orions, the 1K is the brawler variant of the Orions with 4xE, 2xM and 1xB hardpoint layout. You can easily do a 4xML, 2xSRM and an AC20 build and this is a monstrous combination that only the AS7-RS can replicate. Its quirks are a bit borked right now, but when it receives the second pass quirks, the ON1-K will handily topple the Protector as the supreme IS heavy brawler.
Assault Bracket — BLR-3S
The 3S is a 'Mech I've been enjoying immensely lately. Unfortunately its prohibitive cost (11.5M) means this variant isn't for everyone. With this sale however, there's no reason not to get it. It gets ridiculous MPL quirks (even better than the 5SS, except the range) and it's the only BLR with the good torso twist range with 6xE in torsos.