I totally agree with AEnimic, JC wld be best, unless ur ready to forgo uni and go into the workforce immediately after NS. Poly is easier to attain Diploma, but if even if u do well, u aren't guaranteed a place in uni. Whereas for JC, if u do just average, say 1A 2Bs and 1C, u still stand a better chance of going into a uni. I also did my 'O's last year, and i was temporarily fooled into thinking poly was fun. I considered it, but after my teacher's advice, i was convinced to go JC no matter what. As it turned out, i attained 8 points and will most likely enter ACJC. Sure, it may be harder than poly, but life isn't a bed of roses, and its something u won't regret. I had a friend who got 9 points of 'O's and he entered SP. He did well, but could not enter a local uni. Hence, he had to fork out cash to go overseas.
Bottom line: if u want uni, JC. If u don't want, poly. No offence to the poly ppl here, its jus a generalisation for the benefit of my fellow 'O' levellers.