If it's low sodium, then it should be fine. However, frozen will provide more nutrients. A lot of the nutrients in vegetables goes into the water when you boil them, which is why you should steam or microwave them. As much as 40% of nutrients are lost to the water. The same is true when they are stored in water in a can for a prolonged period of time.
If you have the freezer space, I say buy frozen. Frozen is actually more nutritious than fresh vegetables because they are usually picked at their most ripe point, whereas fresh vegetables are picked early and aren't allowed to ripen on the plant prior to shipping to the store.