Shimano 105 is widely considered the best value in road groupsets, and for most riders, it's genuinely all the drivetrain you'll ever need. The current 12-speed version delivers shifting performance that's remarkably close to Ultegra and Dura-Ace — you're not sacrificing crispness, reliability, or gear range in any meaningful way.
Where higher tiers pull ahead is mainly weight savings and the option for electronic shifting (Di2). If you're racing competitively or just want the convenience of push-button shifts, Ultegra Di2 is worth considering. But for recreational riders, club cyclists, and gran fondo participants, 105 gives you roughly 95% of the performance at a fraction of the price.
The money you save by choosing 105 over Ultegra is often better spent on upgrades like wheels or a professional bike fit — things that will make a bigger real-world difference in your riding experience.