i think Poslaju is the cheapest so far. I've been using that for the past 1 year ++ , none of them lost. but sometimes it can be late..up to 7 days.

for items 2-3kg i normally use Citylink. they have flat rate of RM15.00 for that. (only for WM).

both have tracking number, so you can give that to your customers for tracking purposes.