I've used both programs, and am quite skilled with both, here are my observations, obviously I am leaning more towards L2.NET, but these are true facts.
--L2walker--
made for retail
made by chinese people
lots of botting options
limited scripting
limited protection bypass
limited handling in game
detected in most servers
outdated packets
needs lots of 3rd party patching tools
--L2.NET--
made in the USA
made for retail and private servers
in development constantly
wide scripting range
all in one, patcher, packet analyzer, packet patcher and modifier, bot
limited GUI
ease of most private server connection
constantly improved
quicker then walker in many areas, including the autofighter
packets up to date and undetectable for the most part
free for the most part
ready for improvement