The on-site opportunity depends upon the project itself. If you're working good enough, and your impression is good with your senior project managers, you can ask them to consider for on site. The work life balance also depends upon the project itself. The project which I worked upon had a chill vibe. But some projects have some micro management issues.
Basically, it's 50-50 in each company.
Overall i will rate Ibm as a very good company as because you are free to do as much as certification possible, and Ibm will pay your rewards for completing certification as well.
IBM is a brand name, and it reflects when you switch to other companies.