With my Rainbow Crow I made a few builds that I think made effective use of the 'group of eight' quirks (10% energy range and 15% missile cooldown if memory serves me correctly). That right arm is damned near useless though, so in all my builds I just stripped it down to 1 armour and used the other hardpoints. If they want me to armour the right arm and use it they'll need to put a significant UAC2 or LB2X quirk on it, or release more ballistic hardpointed omnipods (Fenris L) so as to boat machineguns.
LRM15/HML Rainbow Crow Can also vary it by losing Artemis, swapping the HMLs with ERMLs (though the left arm has a heavy laser quirk), or going for half-ton lasers and adding more LRM ammo. I liked this one because I felt safer in the 300 to 400m range where it was doing effective damage.
ATM9/HSL Rainbow Crow This one relies on the ATM9 for damage - it worked well for me but a couple times I was pressed as mechs closed to get inside the ATM's minimum range leaving me with just small lasers for defense. The Ice Ferret's good speed allows breaking away back to teammates when that does happen though. It does solid damage if you can keep within the ATM9's maximum damage range.
2 HLL Rainbow Crow This can cause a lot of hurt if you're able to avoid drawing attention. Had a really good game with this one on Polar Highlands where I flanked the enemy and just kept firing from the side. You can also drop the heatsink and add an SRM2 with a half ton of ammo just in case you draw someone's attention - the SRM2 can annoy anyone attacking you while you wait for the HLLs huge cycle time.