msfencode classification

[Dont Know <dkn4a1 () gmail com>]

hi list,

sorry, if it sounds sort of noob-question
but, is ther any kinda classification-table to use encoders?

as, wen I use msfpayload to generate payload, it works perfect, but wen i want to use msfpayload and msfencode together 
to encode the payload, it works only once in 10 attempts

is ther any classification of that kind, or some technique, to help to use correct encoder for specific payload, as 
well, the number of iterations for good scope of success result.

thanx in advance
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