I'm not deadset against LEDs but I find the ghosting prohibitive on most of my older games. Nothing worse than having an insert half lit when it's supposed to be off. My Williams IJ came with LEDs and that's the behaviour it exhibited. Perhaps some of the more expensive LEDs can correct this, or non-ghosting game roms??
But mostly, it's the soft rise and fall of bulbs that I like. The cascading of lights looks best with bulbs IMO. Rapid on/off flashing of LEDs becomes bothersome to me (STTNG with LEDs previous owner installed was really bad). If I find I cannot track a ball, losing it in the strobe effect of LED insert lights, out they come.
No question the LED bright white looks much nicer that the yellowy white of bulbs. Colours really pop with LEDs in attract mode but they are not so compliant in game mode. TOM is a great example of this.
I think some games take well to LEDs. DM is one I've heard. Congo may be another. But for now, I'm sticking to coloured incandescents.
BTW, I've seen WOZECLE in person. Now that is how leds should be done! Very smooth, gradient.... perfect! Obviously a true bottom up design with LEDs in mind. The future looks good for LEDs when implemented like that.