The micro SDHC simply refers to the higher capacity cards.
Buy the largest you are willing to pay for at this time. It looks like you can get an 8GB right now for less than $20 but the 16GB is still around $60 so unless you have an immediate need for larger card, I'd save the bucks (which I have so far) and wait to purchase a larger on when the price drops. Be sure to include shipping costs into total cost to determine what you are paying for it. I've found that on Amazon, anything that says "bulk packaging" is usually less expensive than "retail packaging" and it's the same thing. (I think this is usally on San Disk where I find this.) No need to pay extra for the packaging.
As far as brands, I usually stick with SanDisk or Kingston. Looks like Kingston has just released the 16GB cards so now that they are available from someone other than SanDisk, I would expect to find better prices soon.