OSAL Timer update using main clock/MAC timer/Sleep timer

I have Z stack 1.4.3-1.2.1 and I know the TIMAC also has been updated several times, also according to recent post in e2e. I found there are 3 ways to update OSAL timer.

1. using main clock tips. setup T4CC0 register value to 1ms tick.

   halTimerSetCount() in HalTimerStart() will direct set this value.

2. using MAC timer 320us to update OSAL timer.

    The count of 320-usec ticks is converted to msecs and used to update the OSAL clock and Timers by invoking osalClockUpdate()

3. Using sleep timer to update OSAL timer

    you'll never lose time because that thing is always ticking - even in PM2!

    http://e2e.ti.com/support/low_power_rf/f/158/p/143229/517548.aspx#517548

I have a OSAL timer slow down/slip problem. My current Z stack uses method 1. So I think there is some shortage. But could some one tell me what is the shortage? Also it seems method 3 is the best, but is there any bug in the method 1 and method 2?

Thanks

Rui