East Africa vs India

if you are talking principally about trekking,I'd look at Nepal more than India.....Nepal is cheaper,easier to set up and has scenery at least as good if not better than the Indian Himalaya.

You will meet more travellers in the Himalayan region than in Ethiopia and it is very easy to just travel around without much pre-planning (unless you want to do more technical climbing etc.)

In terms of cost,Nepal is cheaper for sure...certainly Ethiopia is not expensive (much less so than Kenya).

Another thing to consider is when you want to go...climate conditions...though both possibilities are at their best outside of the European summer...I'd try to avoid July and August (particularly in Ethiopia,as the rainy season there makes travel and trekking etc. difficult at that time)

I've been to India as a solo traveller - I'm female - and my last trip I did on quite a thin shoe string. Flights included, I got around on under $2000 aussie dollars for two months. If you're happy to rough it a little (i.e. rooms with no air con or TV, maybe a bucket shower, or a shower with only cold water), then it's dirt cheap and still a lot of fun. I did it all on the fly, no booking in advance, in peak season, which only proved to be a problem at Christmas and New Year when I wanted to get to Goa. Otherwise, it was no problem.

Depending on the time of year you go, India is a great place to meet other travellers if you wish. Alternatively, if you go off the beaten track, you can go weeks without seeing hardly a single foreign soul. It is definitely a challenge, it is like nothing I have experienced before, but when you make it out the other end unscathed, it is totally worth it.

its a hard call..
Ive done both E Africa and India / Nepal, they are both fantastic.
If your only comparing Ethiopia with Nepal, then Nepal wins the argument hands down.
If your prepared to travel E Africa (Uganda, Malawi, Mozambique, Tanzania) then I would go for Africa.
India has lost alot of its charm IMHO.. Just returned to India after a 15 year break and wasnt impressed.. They are moving along in leaps and bounds, good luck to them, but thats where the charm and mystique has been lost, i reckon.
Africa still has the raw energy, the struggle, the sights, sounds and smells that conjour up adventure.. The African people are friendly, smiling and overwhelmingly wonderful..

A tough choice to make.. best of luck.

I just did both this year. You could do both, too. It was less than $300 to fly Nairobi-Mumbai.

I would definitely go to Tanzania and I would also recommend using these guys - http://www.volunteerhq.org/

really affordable and will even cut your costs in Kenya (if that is where you decide) If you want to "get away from it all" they have programs in remote kenya working with Masai people. Other than that I would suggest looking up eco camps in Kenya. They aren't too expensive and are usually helping the communities they are in.

surely india will be cheaper than kenya
http://www.flickr.com/photos/himalays/

I would recommend http://www.crosscontinental.org
This organization offers affordable and flexible volunteer abroad and culture abroad programs in Asia, Africa, and Latin America. It is the best yet the most affordable way to see the world. :)