You have plenty of options when it comes to long term public storage solutions. To help you decide which is best, you should first make a list of what items you need to store and for how long. When you have the worked out, you will be ready to compare the different possibilities.
One thing that is important to determine is how often you will want to access the unit. If you are just putting things into the space and leaving them there, the location becomes less important. You might be able to pick a place that is a little out of the way that will therefore be less expensive.
On the other hand, if you are planning on taking things out and putting things in on a regular basis, it will need to be convenient. If it is on the way to other places you go regularly, such as when you do errands, even better. A cheaper place that is out of the way will end up costing you extra money in gas.