Outside of being the worst defensive type, Ice is decent offensively, and has a useful SE against Dragons. Not to mention it's somewhat the most common 4x weakness, due to the large number of dragons. I'd say the worst type is Poison. It doesn't get SE on almost anything, and doesn't seem to have any notable resistances outside of Fighting. Dragon is a rather good type, having a nice amount of resistances, and being only resisted by Steel, BUT, Dragon is only SE against Dragon, which is somewhat of a downside.
Psychic hits pretty damn hard. Even after Gen 1 stopped it from being OP. Its not hit for SE by any common attacking type. Its only resisted by steel and itself, and it hits arguably the best attacking type in the game for SE damage.
Not to mention Magic Guard and Magic Bounce.
Not changing this sig until we get a new main series Tales game released on a Nintendo console in the US