cadence in bike training

Neither. You do have a natural cadence, that's where you are going to be the most efficient at. There's nothing wrong to do high cadence training, but that's going to be fairly short intervals.

Most efficient will be somewhere in the range of 75-105rpm.

I would say just spin at the fastest comfotable possible. You'll get better as you relax and put out more power. Dont overthink that cadence.

thanks to all guys.
I'll go with the most comfortable gear that allows for the most comfortable cadence.
eventually with practice this will translate to higher power!

IMO it is both. In general, most of my training is done between 90-95.
Twice a week I do what I call big gear intervals where I go all the way down to 60 for cadence. This is not aerobic. I do this purely for leg strength. Meaning, I keep HR under control. During these intervals my watts will go up about 150 from the level at normal riding of 90-95. I also do what I call sprint run ups. These I will go one or 2 gears harder than normal riding but ramp it up to about 110-115 and go for about 30-45 seconds. These are very much aerobic and HR spikes.

You need to be doing different things at different points of the week, and different times of the year. Don't get stuck just training at one cadence, it will come back to bite.
PS One leg (on trainer) spins help to flush out dead spots in the pedal stroke and makes your cycling more efficient.

Same here. There are really three different types of cadence you might use in training (or that I use, at least):

1. Typical cadence that works for you for efficient, sustained power at the race distances you are training for. For most people that is in the 80-95 RPM range. Might be a steady ride or intervals.
2. High-cadence spin-ups in a lighter gear to work cardio system; get heart rate up, often as part of a warmup set (100+ RPM_
3. Big-gear work at a lower cadence to work on leg strength. (50-70 RPM)

Not sure about some of the previous post. Are the numbers you give actual watts, or % of FTP (threshold power)? The latter would make more sense. Also, when you say aerobic, I think you mean anaerobic and vice versa. Steady riding and the big-gear work that doesn't lead to big spikes in heart rate and heavy breathing would be aerobic. Sprint run-ups that spike heart rate would probably be aerobic.

To previous post: good catch on the one point. What I meant to say is both are aerobic. However, neither is anerobic, at least the way I do them.

This is an interesting read on the subject: http://trisutto.com/low-cadence-triathlon/

It really depends on the what you are trying to accomplish with your training session. Slow cadence is great for building leg strength. High cadence is great for improving neuromuscular system. Both should be done as intervals and can be accomplished aerobically or anaerobically.

If you are looking to increase your "natural cadence" (if you know what yours is) you can practice and become more efficient at that cadence (same with run). I found that when I increased my cadence from low 80's to around 90 that I was definitely able to run better off of the bike, but that is just me.

I agree with you.