Beast Master Hunter - tamed a few exotics for PvP/PvE so more utility pets than available to Marksmanship/Survival i.e. Water Striders for water walking.
Rogue - With Vanish back in the <= level 20 stable, quality of life for this class is kind of back. I am hoping that Pick Pocket returns to <= level 20 one day like it USED to be. Or Pick Lock based on Rogue skill and not character level, especially when yet Blizzard gives some non-Engineering professions an unlock perk of up level 50 lockboxes that <= level 20 characters can use or Mechagnomes get a lock pick by level perk equal to Rogues as one of their racial abilities
Monk - Windwalker/Mistweaver just for giggles. Well mostly for their teleport as besides Death Knight, Mage, or Druid or if a VET Dark Iron Dwarf not many classes have a natural teleport ability. I find with F2P being able to get to Legion to bank and hometown portals to other portals, having as many teleports as possible just helps you get things done that higher levels tend to take for granted if they can ask a mage to port them or such. F2P with Gnome/Golbin engineering can get two additional teleports into the mix.
But one all-star class is Restoration Shaman (until a nerf), can heal and range DPS without much gear swapping as mentioned
@Zany but there is also the Druid but can requirement different gear sets to switch in/out when changing roles.
Honorable Mention ---- Best QOL IMO is Goblin! As they can be Shaman/Rogue/Hunter/Etc. BUT also, they have a 30-minute banker NPC as one of their racial abilities as well as getting Exalted pricing most of time as another perk (there are a few faction or non-faction vendors do not honor the deals).