My choice for best steamer is old school...a simple bamboo steamer basket. This particular one from Joyce Chen is just $14.99 at Amazon. It consists of two stackable baskets of woven bamboo. I have found that each basket can hold 12-15 potstickers each, so whipping up a large batch for a family dinner or snacks is a breeze. The domed lid traps the steam, so your items cook faster (it only takes me about 8 minutes to steam a couple dozen potstickers).
You simply put the baskets in a pan of boiling water. The kind of pan does not matter....it can be a wok, a stockpot or a fry pan. While a lot of people like to suspend it over the water, I just set mine right in a fry pan full of boiling water. You choose what works best for you.
It's great for fish and veggies. It's also a great way to heat up and moisturize a dried up bagel or several slices of day-old bread. Amazon carries a bunch of different models. Here's the link to the Joyce Chen steamers: