I own a diesel Ritz that has clocked 20k kms
Total of 7k I have spent on maintaining in 2yrs. 20k service costs 5k , because they change most of the filters.
Totally reliable and trouble free experience.
My parents own a diesel Swift at home, which too is too good.
Ritz is more mature and refined in terms of handling , spacious too.
Ritz is slightly more comfortable on highways and long journeys compared to swift. Swift is more suited for city driving.
Other than ford Figo no other diesel hatch comes so close in decision making. It has a poor ground clearance, non power Windows at rear.
My advice would be
Swift
Ritz (if don't want to wait)
Figo
Take a test drive of all the three before you decide. Especially Ritz !!