Welcome to Android Central! Check the specs on your device--it should say up to what size of microSD card it will support. On most devices, you could use even larger capacity cards, but they're not always guaranteed to work--you might have more chance of corruption. In general, every device should be able to support up to 32 GB. Budget devices might not support bigger cards as reliably.
When shopping for a card, stick with well-known brands, like Sandisk, Toshiba, Samsung, and PNY. More importantly, stick with reputable sellers--be careful with random sellers on eBay or the Amazon Marketplace, because you're more liable to get a counterfeit card. You can check to make sure a card is really what it says it is by running the app SD Insight.