Cocaine is a short-acting, powerful euphoric stimulant. Some people feel extreme confidence and a great ego boost while under the influence. I personally find the high from cocaine - even pure - boring when insufflated, but when smoked as freebase it delivers a powerful rush, and the rush from mainlining gives a heroin shot a run for its money. Cocaine can make you horny, and may delay ejaculation, but with too high a dose you may be unable to get or maintain an erection, and may have difficulty - or no interest - in ejaculating after a while. At least that's my experience.
Cocaine has a fairly easy comedown unless you've been binging, but after a long session the stimulation and crash is quite devastating, and you may be unable to sleep for 3-5 hours, despite the effects having worn off ages ago. Tolerance builds incredibly fast; you will need to increase the dose almost constantly and very soon larger doses will do little to improve the high. Cocaine is also, especially when smoked or injected, ridiculously addictive. I have tried over 70 different psychoactives and NOTHING comes close to the addictive potential of (crack) cocaine. It is psychologically addictive, producing immense and inexplicable cravings for the drug, as well as paranoia.
MDMA is an intermediate-acting stimulant/empathogen. You will probably feel a sense of euphoria (although quite unifaceted - "Yay, I feel great!"), and notice yourself becoming much more empathetic towards other people, often wanting to talk endlessly, and to hug and touch and tell people you love them. It also enhances music quite a lot, as well as dancing. Smaller amounts are great for intimate moments with a significant other, though often it feels better to just cuddle and meld into one for hours than have sex - which can be problematic if you've taken too much, as almost all stimulants are vasoconstrictors, and have a tendency to cause what is scientifically known as the "Scared Turtle" or colloquially "the shrimp". MDMA, unless taken in large amounts or dosed repeatedly, produces a fairly mild comedown, simply noticing the effect has quite suddenly worn off. Greater use may lead to a very depressed state. You may also find yourself being depressed or upset about the smallest things for no reason 2-4 days after taking the MDMA ("Tuesday Blues"). MDMA is not very addictive, but most people find that frequent use leads to highly diminished rewards, and the general trend for the pleasure of rolling seems to be a gradual, constant decrease - you have less fun each time. It also causes unpleasant chewing of the cheeks, jaws and such, which may lead to chipped teeth or aching jaws the following day.
Methamphetamine is amphetamine on steroids. At low doses it's a powerful and very centrally acting stimulant, but at higher doses it becomes a euphoric, recretional stimulant with little application for intellectually demanding activities. You can focus, but it's better suited for fighting a war or helping a friend move houses. Or partying. It has an extremely long duration when taken orally; the main active metabolite, amphetamine, peaks at after 10-12 hours, and amphetamine itself has a half-life of over 10 hours. You can easily stay awake over 24 hours with a reasonable-looking parachute. Sniffing shortens the duration somewhat. Smoking produces an intense, rushing high, somewhat like freebase cocaine.
Meth in general has euphoric peak effects for 4-8 hours, followed by at least 8-12 hours of overstimulation but little pleasurable effects. The desire to redose becomes great, and this is what makes it so addictive - it's a little like cocaine in that sense. Methamphetamine also makes me hypersexual, so if I'm home alone tweaking I may just sit there jerking it all night. No kidding.
I don't particularly like any of these drugs. Cocaine yields a satisfying (albeit short) high when smoked or injected, as does smoked methamphetamine, but the smoking methods are too addictive, and I nearly died injecting blow, so fuck that.