Hydroxycut and Xenadrine contain the same core ingredients, and you're really just paying for hype. I personally like ThermiCore (Met-Rx) because 3 tabs equal one full dose, and I can bump them 2-3 hours apart to minimize sides and the eventual crash. The ad says it supposedly lasts 8 hours, but the CNS stimulation and appetite supression doesn't seem to last longer than any other ECA. You can find it way below retail on eBay if cost is an issue - $14 for a 120 tab bottle. Not bad.
What I _really_ liked, even though it's not ECA, was the old MD-6 formula. It had PPA, yohimbine, guggles for your thyroid, and a couple of other bells and whistles. No appreciable crash coming off, even after several weeks' worth of receptor attenuation. It's a shame they're not producing it anymore. Good luck with your ECA hunt, whichever you buy.