Funny invictus you've got pretty much my mech preferences nailed down.
the Osiris A prime is a good little brawler, the paper armour is frustrating but the mech itself is quite fun to pilot, it's nippy, fast and can sting pretty hard with it's lasers and SRM6.
I prefer using the iPoke Uziel (A) instead of the prime, though the cockpit shake is jarring it's worth it to duel light mechs with your dual lgausses. I tend to use this as a mid range brawler instead of a sniper (stupid but fun and surprisingly effective...)
Love the Bushy A, B and the lbx Scat, but I've been over using them lately. I've tried to use the suicide wagon Holly's recently, the UAC20 one is fun, but it's just far too easy to kill to be effective.
About this point in the match though I normally start getting owned over and over by Clan heavies and assault mechs. As I stagnate in mediums trying to punch above my weight class (and usually failing miserably).
The only heavy mechs I'll touch are the Warhammer and Thanatos. The Thanny C is a favourite, but recently I've been taking the hgauss variant out for a spin. It's quite fun to use, even in it's weakened (balanced?) state, just keep your left arm out of harms way.
My mech selection tends to be on the weaker side, and I rarely take the 'good' variants. I get hopelessly owned as a result but it's a nice feeling when I do manage to take down far superior mechs.
Edit: fixed, Osiris A is a suicide wagon, LBLs just don't seem to work for me...