It depends on many factors:

1. size of your fabrics

2. type of monitoring you want to do

3. how grandular you want to get?

4. Also type of hardware you have in your environment.

If you have large or small fabrics and you just want to get a basic feel for your SAN's then Fabric Manager pretty much has everything you need.

It even has a predict feature that will tell you if thresholds will ever succeed or not which is good if your wondering about bandwidth limitation.

If you have the $$$ in your budget, Finisar does offer Netwisdom which is very good in my opinion as it utilizes both hardware and software tools to accomplish this tasks.

Create a spreadsheet that list all your requirements. Then in each column list the vendors and their products down. Then go thru and ask the vendors for evals and see what you do and don't like about each.

This way you get a good feel for the products and how it may fit your environment.