Sora is not bad quality and as I don't ride in the drops much- The thumb shifter works for me. However I have just gone from sora 8 speed to Ultegra/105 10 speed components and although I did not think I would notice it- The closeness of the ratios on the 10 speed is easier on the legs. The 105 rear mech changes easier on the 105 cassette and the Sora does feel a bit knotchy in comparison.
So Basic unit will be Sora and the next stage up to Tiagra is not a great difference in ridability- However Sora to 105 is phenominal. Smoother and sturdier components. Now Dure ace is supposed to be the ultimate but the difference between Ultegra and Dure ace is not a great deal except in cost.
Depends on your wallet. They all work and there is an improvement as you go up the scale. Its just that some work better than the others.
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How long was I in the army? Five foot seven.
Spike Milligan