Prime is boss
A is BEAST
B is meh
C is aight
There are things you can do with the Thor that you CANNOT do with other clan assets around that price bracket.
The Thanatos is similar, but it's supposed to be, it was based of the Thor after-all and shares the price brackets.
The Thor only really suffers from lack of variants at the moment, and by that I mean lack of D and E variants.
Imagine the Thanatos without the D and E... yeah...
In the Prime you need to buy one ton of LRM and one ton of LBX. Basically you need to be firing at something every moment, spam those LRMs, if you see someone camping in the distance while closing in on a brawler just fire off a salvo and it may very well hit if they dont move. Fire off that LBX at 300m~ too, don't wait until you're spitting distance. Also you need to master hitting point blank with LRMs, you get some beast damage and good mobility in a brawl if you can pull that off consistently.
The A is simple, UAC20 and win games.
B is bleh now, I never take it anymore, HLL are not really worth it in single packages at the moment and it would probably be better off with a couple HML instead. This thing used to be almost as good at the A but then Heavy lasers and ATMs both got nerfed so now it isn't really worth it. I might try it again to reassess.
Take off that LBX20 and put a Gauss on it and we have a deal.

The C is... weird... it has some nice firepower but its hard to poptart too much with it as it gets hot quick even with its DHS. The LRM20 is nice but honestly since you never brawl in the thing it actually hurts, as LRMs really hurt point blank. It is so expensive that people are right in saying there are better options in that bracket.