I have several fixtures that use 3 T-8 bulbs, and also have a few that use 4 T-5 bulbs. I'm happy with both. I tend tend to use the T-5 fixtures for larger plants that I'm overwintering. I have a combination of cool/warm bulbs in those.
But--my T-8 bulbs are real workhorses and use all cool bulbs. In spite of that, I often have plants flower under those lights. I think the important thing is to have a good reflector. My fixtures have a nice, wide reflector, so I can put my 1020 flats 4 across on a 48" wide shelving unit. The seedlings at the outer edges still do very well. I use chains and s-clips to raise the lights as needed.
All of my fixtures are 4' long, and I keep them on 16 hours on, 8 hours off during the growing season. I grow about 1000 plants from seeds each year, and my simple set-up works very well for me.
