Heart rate zones, which should I use - resting HR or lactate threshold?

There's not a huge amount of difference between the two. It's too easy with these device to work to a degree of precision that is unrealistic. In reality you will will operate within a band that is at least 10 beats wide. it's unrealistic to work with smaller ranges due to heart rate lag as much as anything else.

Ok....
So which option do you suggest?
Which is more accurate in your opinion?
:)

In my case HR values are quite similar between %LTHR zones and %HRR zones, 1-3 beats max diff on each zone.

But the zones based on maxHR are way off compared to the other two methods, they are around 20 beats lower except for 90% in which there is 5 beats difference.

To be on the safe side I'm using %maxHR because it has the lower values, since I dont know if I can trust LTHR or RestingHR values, since they have such a difference with the maxHR that is based on my age (45).

I would also appreciate any input on what to trust.

Any HR zones need to be based on real values, not estimated values. If you have a real HRmax value then values from that are good. However, if they've been estimated from a formula such as the most common 220-age then yes, zones could well be lower. For %HRR where did the HRmax value come from? The formula for %HRR is ((HRmax-HRrest)*desired%)+HRrest. Did lactate threshold heart rate come from the watch? In which case that might well be the best one to use.

So, use the zones that are derived from calculated values from the watch rather than estimated values.

Both results (rhr and lthr) come from the watch.
:)

Mine too, LTHR and HRR come from the watch, and MaxHR just comes from the 220-age formula. So will trust LTHR zones then since eveytime its measured it has always been pretty consistent at 160-161. thanks!

I may be influenced too much by the only book I have ever read on the subject, "Total heart rate training" by Joe Friel. He heavily advocates LTHR based zones - and actually says that a sane person should avoid trying to find his max HR.

Anyway, if we look at it logically: There is probably a lot of difference between training above or training below one's LTHR. And one's LTHR is not a fixed percentage of one's max. HR. For one person, LTHR can be 85% of max. HR, and for another person it can be 90%.

So if two persons follow the same max. HR based training plan, and both train at a heart rate of 85-90% of their max. heart rate according to this plan, then one of them may be training above his LTHR while the other one may be training below his LTHR. So one should think that they would get very different results from their training.

If they instead both trained at 95-100% of their LTHR, there would be better chance of both persons getting the same results from their training.

In the above, I assume that both persons actually know their max. HR. If they are using an age based formula, then they are throwing an even larger uncertainty into the equation.

So in my imagination, zones based on max. HR have probably become popular because people didn't know their LTHR. They have not become popular because they are better. So when we actually know our LTHR (assuming that our watches do a good job of measuring it...) I see absolutely no reason for using max. HR based zones.

(But I am absolutely not an expert on this. I read one book...)

Yes, you are right but... :)
There is 3rd option which is HR zones based on RHR

So...
1. HR zones based on formula 220-age (I don't like about this option)
2 HR zones based on LTHR
3 HR zones based on RHR

My question is: option 2 or 3?
:)

When I look in Garmin Connect, there is not an option based on pure resting heart rate.

There is an option based on heart rate reserve, where one end of the range is defined by your resting heart rate, and the other end is defined by your max. heart rate. I can see the sense in having the lower zones defined by the resting heart rate, but since the upper end is still based on max. HR, I wouldn't use it.