Microwaves - 3 popular types in India based on action
1) microwave
2) microwave + grill
3) microwave + grill + convection(fan)
Cost increases in same order.
Capacity ranges from 20L to 32L last I checked(you don't get large size 40L and above microwaves easily in India).
Three types of microwave interiors
1) Heat resistant ABS plastic - cheap, easy to clean, gets dull after a while
2) Steel - looks good, ok to clean but needs constant cleaning to keep looking good, good wave reflection to cook food faster.
3) Ceramic - easy to clean, unclean microwave does not look that messy, gives a good look and feel to the microwave interior.
2 types of exterior finishes
1) Plastic - low maintenance, looks quite good if properly designed, cheap, more models available in plastic.
2) Steel - expensive, fewer models and options(in India), posh looking, must be careful around kitchen to avoid scratching the finish.
Note: All the above are based on research I did two years ago. There may be some mistakes and what I've stated is to the best of my recollection.
Look around at different stores four yourself to get a better idea and make a decision.