In my personal experience using thermogenics / fat burners i've personally found the EC stack to be the best, so yea basically ECA minus the asprin (for those who couldn't put 2+2 together) there's alot of discussion on if you should or should not use asprin, personally i get stomach pains from the asprin so i've left it out.
In terms of dosing for eca, you should start off alot lower to test your sensitivity to it, but the general effective dose is 24-30mg ephedrine hydrochloride and 200mg of caffeine, 3x per day, some people prefer 2x per day because of the nature of ephedrine and it's ability to keep you up all night! I'm personally fine with the 3x per day, seperate the dosing around 4-5 hours apart, and try to keep it maximum of 4-6 hours before you go to sleep. It is very arkward to get the balance right of when to take it etc, but it all falls into routine.
How long should you run it? well once again there are so many options and opinions on the subject, personally i'd run it for 3 maybe 4 weeks max at that sort of dosage, but some people have ran the stuff for months... i would really not reccomend any more than 4 weeks though solely because your body may become very resistant to it, and not to mention when you come off you crash pretty hard from the caffeine suddenly dropping, sometimes it's actually worth tapering off the caffeine... you can come off the ephedrine straight away after the 4 weeks, but it might be worth just using 100mg of caffeine 3 times a day for a couple weeks after to help stop you crashing so much, that is solely my 2 cents though! Everyone seems to do things differently!
I have also used clenbuterol! on it's own and stacked with t3! I personally wouldn't reccomend it because i can't deal with the shakes you get on clen at the higher dosages, i work with people and having hands which shake like mad is never a good first impression, but once again this is based solely on personal experience, you may be fine.
tl; dr
EC Stack imo works very very well with good nutrition and morning cardio, or ECA if you want to include asprin
Clen works well on it's own, rough sides imo
Clen and t3 works amazing but once again, rough sides imo.
Really hope i can help you out here mate! Remember, Nutrition is everything, these are just tools / icing on the cake to help you rid of the last little bit, and they should NOT be used as an effective short cut, Diet + Training is number one and that falls for everything.