Best Fluorescent Light Bulb

I have not upgraded to power compacts yet. I still am using good old tube fluorescent light bulbs.

I have two - 30" fixtures.

I fixture has 1 - 20 watt bulb. The second fixture has 2 - 20 watt bulbs in it. I converted it from one to two bulbs.

So, who makes the best bulb? I have been mixing and matching for awhile now. I am trying to grow plants (which is difficult because I only have 60 watts for a 37 gallon tank).

Does anybody have any recommendations - Brand or manufacturer? Another question - How often should I replace the bulbs?

Thanks for the help!!!!