I am bit confused on what to put - 'a' or 'the' before "better"
- better life
- better job
- better work
For better, there is another consideration that depends on the context of the situation. That is, it depends on the way in which you consider that life, job or work to be better.
For example, if Company A offers you a job that is more enjoyable and pays more than Company B, you are faced with a simple comparison. You might say:
Company A is offering a better job than Company B.
If Company A paid less than Company B, it's still a simple comparison (English-wise, anyway), and you can use the same sentence if you preferred Company A overall.
On the other hand, if you are contrasting an honest profession with a disreputable one, you're invoking something like Kant's categorical imperative. There's really only one choice that can even be considered good. In that case, you would use 'the'. For example:
Honest living may not pay as well as criminal activity, but it is the better life.