lock diff : cheap/free, will enjoy braking axels (always stress on them, some ppl brake them every 5 mins, others last for years...), chirp in carparks, be a handfull in the wet when you dont want to drift, induce understeer, locker im told is very predictable to drift with as it is always locked so you have an idea what its going to do,
illlegal
lsd: around $1.5K, wont brake axels as much (not as much stress as the centre will open up when not required), wont chirp in carparks if its not rediculsously pre tentioned, will be be a bit more forgiving in the wet but will lock up when required, im told LSD is very nice to drive with better than locker as theres no shuddering at low speeds and what not
not illegal
knock yourself out
note: i dont have either, have driven a car with locker didnt like it, car kept trying to straighten up.