Hi Sriram 

Level of difficulty is almost equal in every branch of Engineering, infact in everything you do . So , you should see what attracts you more from these 2 branches of engineering. the Branch of your interest, potential and skills is going to be best for you.

Mechanical engineering focus on creating technologies to meet human needs. Mechanical engineering is more concerned with machines and their efficiency. 

It takes you towards things involving Machines, physics, Manufacturing and production , liquids, gases and more tangible things. 

Expertise in mechanical engineering is great in so many fields. Jobs are in demand , particularly in Biotechnology, energy industries, Aerospace etc.

Mechanical engineering fields include:

- Mechanics, study of forces and their effect on matter

-  kinematics,  study of motion of objects and systems

- nanotechnology, The creation of microscopic devices.

- fluid mechanics have variety of Applications 

- manufacturing is an important step in mechanical engineering.

 Essence of Engineering is problem solving. Mechanical engineers use physics and science in Designing, manufacturing and maintenance of mechanical devices and systems. 

ECE ( Electrical and computer engineering) deals with Electronics, digital systems , communication , system design , circuits, communication equipments like transmitter, Integrated circuits etc. 

Also ECE opens up great career prospects. 

All the Applications which make our life easier such as radio, television, mobiles etc are designed by Electronics and computer are designed in this branch of Engineering.

Job titles are: 

R&d software engineers

Software analyst 

Service engineer

Technical director etc

Both the fields are career oriented, in mechanical you learn Physical elements, whereas in ECE you learn virtual elements. 

So, both the branches are interesting and difficult, it's upto your potential, skills and interest what you want to choose. Choose wisely and on the basis of subjects of your choice.

All The Best!!