Lightfall is the newest. I hear it's not rated very well tho. Gives you Strand subclass. The Witch Queen, Beyond Light and Shadowkeep are bundled together. Beyond Light gives you Stasis subclass. I'd advise waitng for the bundle to go on sale. Forsaken pack is a separate purchase, it gives you Shattered Throne dungeon and Last Wish raid. All expansions give you access to their respective exotic pools, so you may want to do some research on what piece comes with which expansion, if you're picky about your gear.