it depends if you wanna go uni or not.
for poly students to go uni, it's really not that easy. to enter local uni, you need top grades, consistently for whole 3 years, good cca records too. but if you decide to go overseas, it's not that easy too. for one thing, many overseas unis are not familiar with the concept of our local polytechnics and thus, either reject us based on unfamiliarity or give us very little advance standing so you got to start from first year again. (when you finish poly, you're 20 years old). but if you go australia uni then it's a different thing. please do take note, australia unis are getting more and more expensive, going to uni of sydney costs S$40, 000. im not kidding. australia unis do welcome us local students, you do get 1-2 years off and everything.
but with an A level cert, you have to do well, get a BCC can get you anywhere pretty much and A levels are easily recognisable everywhere.
yes, poly is indeed more fun and interesting and you learn much much more useful and relevant things. it'll be good to go poly if you plan to work after poly, if you wish to go uni, i advise you to suck it in and mug for 2 years and do well.
i took the poly route and realise i should have gone for A levels because it's hard to go uni now, even overseas (except for australia lah).
if you're a guy, go poly and then uni, you'll be about 22-23 when you enter uni. most people graduate out of uni at that age
take care and think carefully k... think long term.