I think Tiagra would be the best route to go. My wife has Claris, which an 8 speed, on her bike but she rarely rides it so due to low miles it still works good. I think if you're going to be riding it a lot Tiagra is the better groupset, plus it's now 10 speed capable and it has shifters that are the same as you would find on 105 and above while Sora is a 9 speed system and is difficult to upgrade, the Sora and Claris brakes do not brake as smoothly as Tiagra and above does but that's mostly because they use a cheaper shoe. But Sora does work and seems to be more reliable than Claris plus it's cheap in price...but Tiagra isn't bad in price either.

The newer Tiagra 4700 did away with the thumb shifter button so it mimics the 105, Ultegra, and Dura Ace levers, whereas the Sora levers retain the thumb shifter button which bothers some people while others don't mind. The odd thing is that Claris uses a similar shift levers as the Tiagra and above levers have, why Sora didn't go that direction is beyond me.

perhaps reading this will help more than I can: Shimano Claris groupset review - Cycling Weekly

I think if price is the big issue for you the new Claris would be a fine option if upgrading isn't something you want to do later, otherwise if you do want to upgrade later than I would go with Tiagra. I don't think going with Sora would give you enough improvement to be noticeable over Claris, so for me personally Sora would be out of the equation, either go whole hog and get Tiagra or be cheap and go with Claris.