Currently doing Thief / Monk, will be
Wood Elf for insane speeds
Thief 4 Shadow Monk 6 / fighter 2
Start STR 15 DEX 17
Level 3 Thief - Two Bonus actions
Level 4 Thief Tavern Brawler STR 16 - Auntie Ethel DEX 18
Level 5 Monk So now you can sneak attack and follow up with two Flurry of Blows / Unarmed strikes at +8
Level 6 Monk - Bull Robe STR 18
Level 7 Monk
Level 8 DEX 20 or Mobility
Level 9 Extra Attack
Level 10 Monk - depending on your monk subclass here; Shadow gets a fun misty step here but misty step is easy to come by. I think I'll go kung fu maneuvers
Level 11 Fighter - Second Wind
Level 12 Fighter - Action Surge
Now. This character is *stupid* fast, and can jump really far, too because you hafve good Strength. Because of thief, you don't have to worry about falling damage much, so you can hop down and murder the fellows below, too. I'm doing this one for a Dark Urge playthrough, and the cloak gives him good survivability, but otherwise this is a glass cannon due to the low HP pools and low CON/WIS for AC. I'm in early Act 2, but he pretty much solo's entire dungeons.
But. You can be *way* out of position, rush across the battlefield, then Attack twice, then do Flurry of blows twice, that's two attacks each - then Action Surge for another two attacks. And that's without a potion of haste.