I haven't used Clen so I'm not going to vote, but I would like to clear up one thing about EC/ECA. It does stimulate the beta-3 receptors. That is why it can be used for so long. Your beta-2 receptors will indeed down regulate after a week or two, and your appetite won't be suppressed anymore. The thermogenic effects however, do not go away, and in fact actually improve for quite some time. This has been shown to be due to continued beta-3 stimulation. It has also been shown to be protein sparing.
I will note however that most EC/ECA studies are performed on obese subjects, and not those of us looking to lose those last few %. I'd post my references, but I'm tired and will be going to bed soon.
Maybe tomorrow.