depends
it depends on which field of work you're interested in and the aspects of your own character you wanna develop. Even if you end up in a school that sux, JC or poly, this conscience would keep you afloat.
But...the point is not to struggle too much and enjoy life. I studied in JC coz it was the "only choice" after secondary school coz poly at that time seemed to be a place for rejects. I later found out that what a few of my friends were doing (they didn't do well in O'levels for L1R5) was similar, if not more in-depth, than what I was doing in JC. Also, I felt that I was restricted to a few choices we had in JC- science, business, arts and other subjects compulsory. The only thing i guess I learnt from JC is the research, thought and argument processes, which in other words, could mean B.S. to many people. It seemed that generally JC students were more articulate than Poly counterparts. Perhaps it was GP, or something else, like cooking up excuses for not following tutors' instructions.
Anyway, in the long run, most of my Poly friends actually excelled in their fields. A lot of it might be due to the relevant practical training that was provided in Poly - the hands-on experiments. That made them very employable. Also, it's not uncommon for Poly grads to be admitted into Uni these days. I've even known people who graduated from Poly, worked 2 years in relevant fields, and got into Masters straight. One of my friends, who failed to get into JC because her languages weren't good enough, is currently doing her PHD at NTU on scholarship. So if you're really interested in a particular field and it's offered in poly, my advice is go for it rather than wait 2 years to get demoralised in JC. If you want the most of it, keep reading critically even though you don't have a GP paper to do.. that'll be a bonus.
PS: my info might be outdated coz it has been ages since I wore that school skirt.