I wonder whether I should buy some antimalarial pills (or whatever) before going to the Southeast Asia. If yes, what's a good brand available in China?
My initiary is:
Malaysia - 7 days
Thailand - 14 days
Cambodia - up to 7 days
Vietnam - 14 days
Laos - up to 7 days
All of it overland.

if you're travelling soon, i.e. winter / dry season, i'd skip the antimalarials. it's not worth the side effects, they're difficult to get in China, and they do nothing against dengue. oh, and there's fewer mosquitoes at this time of year. take some repellent.

I'll start on 9th January.
I only have 30% DEET spray and that strange anti-mosquito thing for the electric plug with some solution inside (though I guess it doesn't work on those killer mosquitoes anyway). Is it enough then?
I've heard about (sometimes) annoying side effects from those drugs, but I've had no idea when is it worth using them nevertheless.

Hua Lu Shui (flower green water) made in China available in any super market.

One variety is anti mozzy. Cheap and effective and I don't think it contains too many harmful chemicals.

No need to buy antimalarials. They're stupidly expensive, their side-effects and impact on your liver are huge and you may never have enough to actually stay a long time.

Yunnan and SEA are considered high-risk zones, but you need to know that a place is categorised as such as soon as there's one (1) deadly case a year. The problem is a lot smaller than the medical industry would have you believe. Dengue is a much more real issue. If you really want to be on the safe side, get a treatment dose (that you take after you think you have malaria instead of pre-emptively) of Malarone and only take it when you have symptoms of malaria.

Mosquito netting and mosquito-repellant, as well as long sleeves etc. are a much more (cost-)effective way of preventing mosquito-borne disease.

OK, thank you all for the help!

I agree with bluppfisk, anti-malarials are an overblown load of BS from pharmaceutical companies trying to make a buck. They are heinously expensive, have bad and long lasting side effects and don't always work. If you are young and healthy and get malaria, its highly likely you will recover from it, so don't worry so much. Like bluppfisk said, dengue is a much greater risk, but both can be avoided by minimising your exposure. If you are going to random places, I would suggest get a mosquito net before you go as out of the way accommodation sometimes don't provide them (covering the bed) or they are old and full of holes. Plus long sleeve shirts and long pants when outside from dusk until dawn backed up by repellent. You will still get bitten a few times but only a tiny percentage of mosquitoes carry the diseases so the chances are slim you will get any infectious disease.

Couldn't agree more! NEVER take preventional malaria drugs, they're a farce, the medical companies inflating the problem to make money!!

If you go to a very high risk area, just take a treatment dose.

With your itinerary, I'd just take some repellent.

Thanks for reassurance!
Maybe I'll just buy a mosquito net because my girlfriend attracts mosquitoes a bit too much, but I guess (and hope) that will do the job.