There are some important things to think about when you're choosing a pet stroller.
size: make sure you measure the interior space available for your pet, and make sure your pet is going to fit comfortably inside. Make sure they have room to lie down, but not too much room or it won't be safe for them.
Intent: what do you plan to do with your pet and their stroller? Leisurely strolls around the block, or active running, jogging and biking?
If you're going for the leisurely stroll one of the classic 3 or 4 wheeled pink pet strollers ~ or any color for that matter will be a great option.
If you're going to be more active you'll need a sturdier, more rugged pet stroller. You can find great jogging strollers as well as pet bike trailers that will convert into a jogging stroller. These are perfect for more vigorous use.