in My humble opinion my choice would be like this

1. PSP (owing to my passion for it)
2. DMG/MLC
4. FSP (its paid vacation.. govt. pays you to go on vacations)
5. IRS (Its a far far better group than Customs now)
6. C&Tg (you can call it a sister group of FSP, work as foreign attache or setup your own business)
7. Customs (post are few now and good ones still fewer, promotions are now extremely slow, highly politicized deptt. in terms of getting postings)
8. PAAS
9. Railway group (has enormous facilities)
10. Postal group (facilities and peaceful job with huge powers like recruiting a 14th grade officer when you are urself in 17th)
11.OMG (you'll be doing the job which DMG people hate to do i.e. moving the files up and down... you'll remain the staff officer of DMG secretaries) mostly
12. Info. Group

The above is strictly my personal point of you.. anyone can dissent from it