As the title suggests, this is a thread describing the differences and similarities between these two shows. Here are a few pictures i put together to help you get the idea.

http://srebak.deviantart.com/art/A-TLA-and-XS-Water-146763531

http://srebak.deviantart.com/art/A-TLA-and-XS-Earth-146764428

http://srebak.deviantart.com/art/A-TLA-and-XS-Fire-146764804

http://srebak.deviantart.com/art/A-TLA-and-XS-Air-Wind-146765253

http://srebak.deviantart.com/art/A-TLA-and-XS-Element-Symbols-146765537

http://srebak.deviantart.com/art/A-TLA-and-XS-Allies-146766150

http://srebak.deviantart.com/art/A-TLA-and-XS-Wisecrackers-146767054

http://srebak.deviantart.com/art/A-TLA-and-XS-Small-characters-146767332

http://srebak.deviantart.com/art/A-TLA-and-XS-Transport-146767606

http://srebak.deviantart.com/art/A-TLA-and-XS-Warriors-Masters-146768094

http://srebak.deviantart.com/art/A-TLA-and-XS-Warriors-Figures-146768543

http://srebak.deviantart.com/art/A-TLA-and-XS-Loving-Fathers-146768851

http://srebak.deviantart.com/art/A-TLA-and-XS-Great-Power-146769099

http://srebak.deviantart.com/art/A-TLA-and-XS-Strange-Realms-146769393

http://srebak.deviantart.com/art/A-TLA-and-XS-Strange-Beasts-146769688

http://srebak.deviantart.com/art/A-TLA-and-XS-Villains-146770119

http://srebak.deviantart.com/art/A-TLA-and-XS-Femme-Fatales-146770351

http://srebak.deviantart.com/art/A-TLA-and-XS-Lesser-Villains-146770582

http://srebak.deviantart.com/art/Avatar-and-Xiaolin-Showdown-146770761

http://srebak.deviantart.com/art/Two-worlds-but-Four-Elements-146770985