Dear Guarnerius,
In answer to your question, a Yamaha is a good instrument, the bigger the better. S series is better than C, although C is entirely fine. Personally, I think anything smaller than a C7 is simply an inferior piano, but I am a snob.
How it compares to Steinway? Steinway is more expensive. You can buy a fine house for the price of an Steinway C. If I have my numbers right, you can buy from 2 and half to three Yamaha C7 for the same amount.
By now you must have figured out I am what Steinway lovers call an "Steinway basher." I strongly believe they are not worth their price, and that there are several better pianos that are less expensive (most prominently, Mason & Hamlin).
Although I disagree with classicarts' logic (while I admire the significant growth that her or his opinions about the various brands has undergone since s/he was asking whether to get a Steinway a Baldwin or a Yamaha, not so long ago), one thing we agree on: you would benefit from taking your time to buy a piano. Develop your palate, read about the various brands and especially try to play on them, and embrace what aesthetic you really identify with.
You may fall in love with the sweet (and to me inaudible) sound of a Bosendorfer, the richness of Bluthner, the projection of Bechstein, the mystery of August Foerster, the competence of Mason, doesn't matter. If you end up loving a Yamaha C5, who can really judge you for not having a more expensive (if not sophisticated) taste? Buy the piano that makes you happy. That's what money is for.
Best wishes,
H
(and to Classicarts, please forgive me for not engaging anymore with you. I find your opinions uninformed and feel you have no interest in exchange of ideas, so I will largely ignore you in the future. Good luck.)