I have both the Cullen Crossovers and TWL "Obsession". I found the Crossover to be wonderful, a real bargain. Then I tried the TWL Seven Plus and was wowed. Over the years I traded up to four Obsessions to handle the line conditioner, preamp, dac and transport. I still use the crossovers for my subs; I doubt more expensive cords could serve them better, and may actually degrade performance.
TWL almost always uses PI Audio Group's Line conditioner. I use it as well. It cuts noise and adds slam. It is a bargain! I also use PI's "Mongo" power cord for my amp, which just works better than the others in that spot.
Patrick Cullen and Pete G. are both great guys and pleasures to do business with.
I suspect that the cheapest TWL will sound better than the Cullen, but it's more money and very dependent on what equipment it is used with and system synergy. Should you want to sell your cord later, TWL holds it value well.
BTW, I just put graphene on almost all my contacts. And WOW! THE BEST BANG FOR THE BUCK! It is eliminates the micro-arcing at contact points. But be careful. Graphene can migrate and create a short.