Context: The terms are used when leaving chat sessions. Some people type deha/wamata and others, jya/jaomata. Which one is more polite?
When expressions are shortened, they are usually considered less formal and thus sound less polite. This applies to
では vs. じゃ: じゃ is less formal and thus sounds less polite (but can sound more friendly). Other common examples include:
しては vs. しちゃ,
している vs. してる,
しておく vs. しとく,
してしまう vs. しちゃう,
すれば vs. すりゃ,
しなければ vs. しなきゃ.