Platina 125 & 100 will give u almost the same mileage because both have almost the same kerb weight(difference is only 2kgs) and power difference is just 0.2bhp. Also Platina 125 has got a five speed gear box, which will give it better performance in city and highway and also good mileage.
So btwn these two definitely Platina 125cc is the better bike. Powering the Platina ES is a new 125cc single-cylinder with Bajaj’s DTSi technology and ExhausTEC. The similar engine also powers the Discover 125M, but in a higher state of tune - 10bhp and 9.02Nm. In the case of Platina ES, the engine is tuned to return 8bhp and 8.7Nm.
In terms of design, it looks largely similar to the current Platina except for new side panels, new exhaust, slightly different headlamp design and new graphics. The vehicle also gets an electric start feature. Overall I would say after buying this bike you can proudly say "Petrol abhi baki hai mere dost".