Anyway my entire kitchen flickers at a high frequency now. (The replacements went over the island.)
Do you have the correct ballast for the correct lamp? Is the ballast wired correctly?
8' t12 fixtures often had the line and neutral wires hooked directly to the tombstones. The newer ballasts are not wired the same. The ballasts usually have wiring diagrams on them.
The t8 lamps put out more light (lumens) than the t12, even with the same wattage. I like the T8 4' lamps and fixtures. You can buy any color lamp you want. I use 6500k lamps in our business work shop, and in the garages. The color looks similar to sunlight. 4100k is my favorite for general business lighting. I can't stand anything less than 4100k as it is too yellow/orange.
T5's are not real common yet. Home Depot and Lowes only had one color available when I last looked for them. They are also pricey. I'm sure an electrical supplier would have better choices, but I worked in many different areas and couldn't use just one supplier.
Magnetic ballasts can be noisy. T8 electronic ballasts are quiet and much lighter. I can change out a ballast 5-10 minutes depending on the fixture. Some are more of a pain and can take longer.
A t8 ballast average $20 bucks when I last bought them.
The dim-able 2pin and 4pn cfls are expensive and can be a real pain. They are used as can lights in many commercial buildings. Those could be very expensive-$80+ for a single ballast. I have had to change a number of those ballasts by accessing the ballast through the 6-8" hole (in the ceiling) that the can light goes in. That isn't much room to work in, especially if you have to change one out that is 277v single phase and is hot while you are doing it.
T12's suck and need to go. I do however understand how many existing t12 fixtures still exist.