Another thing Yamaha has going for them is aside from keyboards they make a wide range of other instruments, so although some might argue against it, they should know more about instruments than Casio since they have such a great instrument production backbone. Must be why they have such better acoustic sounding sounds as Sysryn said

.
I should note I'm not a Yamaha zealot. I just have respect for them.
Atleast, I would make my final decisions based on reasonig like that. Research is still your best friend, find out which models are available, look at the product specs of the ones in your budget range, know what you are looking for(sequencer/synth/sampler/sounds etc...), read lots of reviews(both biased and unbiased), go to youtube or do google searches for sound samples, you'd be suprised what you can find.
The last step is trying to play on the thing before you buy it. Although I can somewhat understand your pain with availability(South Africa ain't that great), luckily most brands/products are available here through one of the shops close by, but I couldn't play on the keyboard I bought before I bought it since it is a hassle to get it here, but it's not like I had doubts about one of Yamaha's best keyboards(S90 ES)

. Youtube helped me there by having quite a few samples with different sounds.
Anothing thing after having a general idea of what is available is to make a list of priorities of features that you want your keyboard to have. For me the Yamaha S90 ES fitted my want/don't want list perfectly.
As a parting note, usually with new computer technologies and hardware, it is a good idea to wait for other people to buy and try things out and let whatever new technology/product gain or lose some respectability(this way you aren't the one paying for making a risky choice). The way it is now, you can't really go wrong with Yamaha. You get what you pay for. With Casio I'm not so sure. Don't know much about them. I suppose my old Casio CTK-481 just left me with alot of negative feeling for them. If I knew what I know now I never would have bought it despite the 2nd-hand discount I got. It really is just a toy.
Ok, second parting note. Don't rush, let new information settle a bit, go over things and such. Waiting a week or two to make the right decision is better than making a bad decision and being stuck with what you bought. I remember going nuts with anticipation and desire, and the delivery time for the keyboard just made it worse, but I have no regrets at all about my choice.
hhmm, I ranted again. Oh well, welcome!