It is very subjective. In essence it depends on what you want out of your life / career. The kind of family you belong to and the kind of family life you would like to have. Your marital status as well as your future plans. Again it is also determinant on your world view and the kind of role you would like to play in that. Most of all it is determined by your priorities.

If the essential social structures in your life allow you / support you to maintain a life style required / expected in FSP then you can go ahead and opt for it. Honestly, i would like to say that every one should opt for the service that inspires them and would utilize and enhance their individual talents to the optimum. But since you have asked for my advise, i would say talk to your family about the choice you would like to make. Tell them the demands of a nomadic lifestyle and frankly a social one to a degree as well. If you get the important people in your life on board with the choices you make, that would serve you the best in my opinion. Please also remember that people change as they grow older and sometimes we may want entirely different things from life to the ones we wanted when we were younger or say in our early to mid 20's.

As a direct comparison of services; FSP against PAS/IRS are completely different lifestyles and not just different services. Joining either of the two will essentially determine the kind of life you live (assuming you want to continue your career in the group you join). Similarly they will also present different opportunities as you go along. FSP will require you to be posted abroad for long stretches and that has its stresses on family life if things are not planned out in advance. As a diplomat it would be your duty to give a certain amount of your time to the service. Similarly, working in the field and a patriarchal social structure of our country, especially the non-urban areas, would have its own challenges.

So think about what you would want your life to look like when you look at it 20 years from now. If like the most of us all you want is a stable job that places you smack in the middle of a certain social stratum of our society then anything works Hope i did not digress too much!

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There is a tide in the affairs of men. Which, taken at the flood, leads on to fortune; Omitted, all the voyage of their life Is bound in shallows and in miseries. On such a full sea are we now afloat, And we must take the current when it serves, Or lose our ventures. ~ William Shakespeare