Maruti WagonR is the odd car out of the three cars. Technically speaking WagonR is slotted in one segment lower as per Indian automobile market classification. Brio and Micra do fall in the same premium hatchback category. Between the tree cars in your consideration set WagonR 2013 at Rs.3.58 lacs is the cheapest with Nissan Micra at Rs.4.26 lacs being the costliest.
Basis your query let's examine each car on your parameter of selection;
Mileage (ARAI) for WagonR is 20.51 KMPL, followed by Brio which delivers 18.4 KMPL with Micra being the lowest at 18.04 KMPL. However, point to be noted that both Brio and Micra ahve a 1.2 Litre petrol engine under their hood vs just 1 litre under WagonR's hood. Mileage for WagonR is bound to be higher.
Strong Body can be measured basis build quality rating for these cars on a 10 point scale is: WagonR is 7/10, Brio is 7/10 and Micra is 8/10.
Servicing and parts cost whilst are not based on actual figures, basis market information and perceptions, WagonR is considered to be least expensive with Micra being the costliest, Brio will however not be very far from Micra in terms of maintenance cost;
Our recommendation, in order of preference be Brio, WagonR and then Micra.
Do treat our inputs as suggestion only and not a final recommendation. Test drive all the cars in your consideration set and decide.