Well, if memory serves per Shimano road components from lowest to highest per price/performance:
Sora, Tiagra, Flight Deck 105, Ultegra, Durace, Durace (Electronic)
Also, these can be in a 2 chainring or 3 chainring configuration (front gears)
I guess it depends on how much riding you plan to do, type (commuiting/recreation), roads (hills? flat?), & budget.
Some casual road cyclists I know have Sora w/3 front chainrings. Those that are into cycling a bit more for
recreation & fitness have either Flight Deck 105 or Ultegra in either 2 or 3 front chainrings.