If you need to be stealthy in your growing process, then you are probably limited to using a closet.  Closets have certain drawbacks: they may be tough to ventilate, they may lack electrical outlets, they may not be big enough, and most likely they are not light tight.

So, if you can get away with having a 3' x 3' x 5'h black rectangle in your place, by all means spend the money and get a grow tent.  The whole growing process is much simpler if you do.

Grow tents are lightweight, durable, have a reflective inner lining to direct more light to the plants--sort of like turning your entire grow room into a giant light reflector.  The frame supports up to 60 pounds of lights, fans, or other equipment.  There are multiple access ports and vents strategically located.  One person setup, no tools required.

You'll want your grow tent to have plenty of space between the tent walls and the sides of your reservoir, especially if you're going to bend your plants in the sea of green method of cultivation. so don't skimp on your tent.  Additionally, you need to figure that the top foot to foot-and-a-half of your tent will be taken up with lighting and the bottom foot or so will be taken up by your reservoir, so deduct two feet (or more) from the height of the grow tent to figure out the maximum height plant you'll be able to grow.

One thing that can trip you up is drainage.  The reservoir drain is located near the bottom of the reservoir.  To drain the water, it needs to be able to flow downhill from the drain.  Depending on your circumstances this may mean you have to elevate the reservoir in order to fit a bucket under the drain.  This will have a corresonding effect on the height you'll need for your grow tent. 

I did my first grow in a closet.  For my second grow, and all subsequent grows, I use my grow tent.  It's just that much better.