It really depends on what is important for you: The suite amenities include priority boarding, tote bag, in suite dining....etc then do the Sky Suite.
The Concierge Class gives you some of the suite options such as: canapés, welcome bottle of wine, flowers, bathrobe etc.
If you book a suite I strongly suggest not booking a guarantee. The Sky Suites on Deck 12 have the large balconies with the SS on deck 10 having smaller balconies. The cabins are identical.
Check out a deck plan before booking.
More information can be found at: Celebrity Century Information
I do not suggest booking a "Century Suite or Sunset Veranda" on Century. The Century Suite is an aft balcony cabin but is not much larger than a regular cabin and the Sunset Veranda overlooks the Sky Bar and is noisy and the veranda is not private.
If it was me I would go with a Deck 12 Sky Suite "if" the price is not significantly higher. If there is a large difference in price I would go with the CC class and have more money to enjoy Europe.