New to Caravanning - Need a Tow Bar

Our caravan is on order so now we need a tow bar.  We contacted our dealer who said we can get any type as it is a hitch?? Haven't got a clue what that means however, on checking the website of our local tow bar suppliers the options showing for our car are detachable, 2 ball flange and swan neck. I think the makes maybe thule and whitter.  wondered if anyone could enlighten me on pro's or cons of the varying types and any preferance.  I have no clue.