I love trains, so on my first visit to Southern India taking the "Toy train" to Ooty was a must.
I had to book weeks in advance to get a confirmed seat, it's an early start from Mettupayalam, and it's not a very comfortable seat for a five hour journey (what do you expect for 80 rupees in second class?), but I enjoyed every minute.
From the sweet nectar of Indian railway tea at every stop, the regular stops to top up the water tank on the steam engine, through to the magnificent views across the valley as you climb, it is an experience you won't forget.
If you have any interest in trains, then this is the perfect way for you to get to Ooty. If you haven't, then you will probably still enjoy the views.
Key tips - book in advance (there are only a few First Class seats so they sell out quickly, and even Second Class can fill up days before departure. The train stops several times, so use the opportunity to get off for toilet stops, buy tea, take pictures, etc. Our trip used a diesel engine from Coonoor to Ooty, so for the full steam experience (and also for many of the best views) you need to get on board at Mettupalayam.