I have only bought the Raven 3L, and i really don't find a reason to buy the other ones, but i also want my 3L to make Elite, but i really don't want to spend C-Bills on the crappy other ones, but finally i will do it to make the grind, but then it would cost me soo much C-Bills to upgrade them to make them playable, but then i don't have the money to buy other more viable Mechs.... aarrgh FTW!
This is a pretty tough question. After leveling my Catapults, I sold my A1 because I never enjoyed playing it. Everything just felt like a grind and it was difficult to damage the enemy. I regret selling it now and I imagine that if I had opted to buy DHS for this chassis, I would have enjoyed it much more than I did, and instead of slogging through grinding XP, the leveling would have been much funner. So now I buy DHS on any chassis that I level. The expense is likely mitigated somewhat since once you upgrade, you will be making more money per match due to a higher damage output.
My biggest regret are my Commandos had a Streakmando that never performed because he had SHS, but I couldn't cram DHS into it and gave up. Now my Death's Knell (a horrible purchase) is so lonely.
DK is actually fun. It is small and agile, and brings in cbills. They really need another light hero though.
It must be me, then. I swear that I earn more via losing in a non-premium 'mech that I do in a victory with Death's Knell.