Not clear if you want new or used. Be aware that Suzuki Thailand are still selling the second generation Celerio. A new third generation Celerio was launched in Japan last year and is on sale in India. Its a big advance in that it uses the 'Heartect' platform of the latest Swift (and other Suzuki cars).
Both the Swift and Celerio use the Suzuki K-series engine. 3-cyl in the Celerio and 4-cyl for the Swift. Its extremely reliable. We have a lady customer in the UK with 300,000 miles on her Swift and the engine is original!
Gearbox is either an Aisin-supplied manual or Jatco CVT-7. The Jatco is the same unit fitted to the Mitsi Attrage, Nissan Almera etc. Not the best but OK if you change the fluid periodically. The manuals suffer from worn synchromesh on 3rd gear but its relatively cheap and easy to replace.
Both cars have cheap and flimsy-feeling trim but it does seem to last better than you'd think.
For me the Swift is the obvious choice if you're going to drive outside the city. Celerio is fine in town but struggles on the open road. The Swift actually rides and handles very well for a small relatively cheap car.