SDHC was the standard for cards up to 32GB. SDXC is essentially the same only for larger ie 64GB cards. I suspect you would almost instantly regret buying an 8GB card as you won't fit much on that but I don't know your needs.
Brand shouldn't make much difference but don't buy a suspiciously cheap one from eBay as it will be a fake (ie it will report that it is 16GB but will actually be 2GB so any data over 2GB you put on it will silently be lost). SanDisk used to have a good reputation but they have produced some duff 32GB and 64GB cards recently. You should be safe with Samsung.
Having said that, any card you buy from a reputable seller such as Amazon should probably be fine. You should probably go for one of the faster cards such as a class 10 card. If you are only buying a small card, it will still be fairly cheap.