If radiation weighting factors for xray or gamma photons or electrons of any energy are 1 and alpha particles possess a factor of 20 why wouldn't it be preferable to be exposed by gamma rays?
Alphas are little trickier in that they are very high-energy, but also very massive. The median stopping distance for an alpha in air is about 20 cm IIRC. So the thing you have to remember with the quality factor tables is that they're for radiation that's already in the body. Alpha emitters that aren't ingested are essentially harmless; they have a quality factor of 0. And like I said earlier, most alpha emitters (and all the long-lived ones) are transuranics. There are chemical toxicities associated with them as well, and they don't play any role in any biological systems I'm aware of. So alpha exposure is only an issue with fallout - if there's radioactive dust in the air and you breathe it or it ends up on crops and you eat it, there could be major health issues. But even in a worst case scenario, Chernobyl-type release (which would be physically impossible in the Japanese BWRs anyway), all you have to do is wear a mask and rinse your food with water, and your alpha dosage drops to zero.
BTW, I forgot to post the link to the *only* news source I've been able to follow that has up-to-date, factual information specifically about the nuclear issues. It's the IAEA's facebook page: http://www.facebook.com/iaeaorg
The times, they are a-changin'...