i see... i suppose in that way, signing on with the SPF/SCDF is better than going with the SAF. Because you'll be on permanent scheme, which means that if you don't get sacked, then you're allowed to stay with the oranization until you retire. but in the event that you do end up with MHA as a regular, do take time out to take up part-time studies if time permits. it will serve as a 'back-up' of sorts, just in case you'd like to leave the sector one day.
in comparison, for regular soldiers, they get paid more than those in SPF and SCDF. but they don't have that 'job security', if you'd like, 'cause they'll be on contract scheme, and their renewal criteria is very, very subjective. but they try to make up for it with better pay and lump sums of cash though.
do take your time to decide what you want to do. I was in 3rd year poly once, and I had no idea with regards to what I wanted to do. but slowly I suppose the path is presenting itself to me.
important thing is that whatever you choose to do, make sure that you're doing it for the right reasons. have the right motivation for anything and you're bound to do well in it, regardless of what it may be.