Big Rig - No
Lockdown - Maybe
Spitfire - No
Diana - Yes
Shellstinger - Yes
F-9 MARK - Definately
Ultra Mutant - Depending on how much crystals / res you got.
Big Rig doesn't do any damage anymore, since both his skills are nerfed so badly, and he only has 7k AGI.
Lockdown is one of the fastest mercs on the X if you POPE the AGI, good first attack merc.
Spitfire, good merc, worth nothing though. Crystals go for 10 vs. 1 AC nowadays, crystals would cost you way too much to build a nice Spitfire.
Diana, has weaken effect ( ? ) and it's a mini Cannonback, I'd say OPE 200cc.
Shellstinger, big weaken effect and a lot of damage, 200cc seems good for this merc.
F-9 MARK, definately worth 400cc.
Ultra Mutant, great merc, low value nowadays on the X since there are so many good ATK mercs out there like Incinerate.