It is a difficult issue to address. First and foremost, you should know what you want. Since it appears that entering local uni is one of them, let us say you finish the first step. But as a local university student, I tell you honestly that if you wish to perform well here, the pressure is extremely great. Even if you are multiple As holder, your peers can often swat you like you are fly in grade not to mention the high influx of briliant foreign-talent.
Second, after experiencing JC for 1 year. How do you find your life? Do you think it is desirable? Do you like the academic system or do you prefer polytechnic system? Perhaps you should pull several of your old secondary school mates who go to poly to describe their life in poly.
Third, let us discuss probability. In JC, to enter a local uni, it depends on the courses that you wish to enter to. Check on the local uni website since several of them put cut-off point of previous intake. Usually, except those ridiculously difficult to enter course such as medicine and its ilks, 3 or 2 As should be safe enough as long the others are Bs and try not to get lower. For polytechnic, GPA 3.4 / 4.0 is often rumoured to be the safe spot and the choice of poly is also crucial. I heard rumours that I cannot confirm or deny that Singapore Polytechnic and Ngee An is the "good" one in local uni eyes.The question is: Which do you think is more favorable to you?
Poly grad life in uni is often simpler, some modules overlap with poly module if you continue in the same course and you can take less module. My friend from poly take 4 modules minimum to graduate while I take 5 minimum each semester for 4 years.
Well, good luck.