We've discussed this several times before on TSR. My opinion, based on 17 years in the RAF and keeping a very close eye on the prospects on my airmen/NCA colleagues wrt to commissioning is that it is not a sensible prospect to join the ranks if you aspire to a commission.
Firstly, if you are genuinely officer material, then you will be like a fish out of water in the early days of your basic and professional training, and are likely to be extremely frustrated with the restrictions and limitations of your job. Like all the Armed Forces, the RAF has a strict hierarchy, and you simply cannot give an SAC the responsibilities of a Pilot Officer, just because they have the potential to manage them. Thus anyone who has officer capacity right now will find themselves severely under used and under challenged as an SAC.
Secondly, there is no real incentive for the RAF to commission you. You are filling a post which they want filling, and they have no particular problems with recruiting Officers from civvy street, so although they will do it, you have to sell yourself to the system and prove you can make it worth their while. Although they might be getting an Officer who is savvy and happy in the system, they are also going to have to recruit another airman to take your place.
Thirdly, the time component. There will always be someone who knows someone who was offered a commission within a year of getting out of professional training, but trust me, this is extremely rare (and I have my doubts it really happens at all, it does indicate a fairly grave failing in the recruiting process). Realistically you are looking at 5-6 years getting absolutely top scores and the necessary recommendations in the ranks before your profile will look at all suitable. Even then, you may well find yourself simply in a queue with senior Cpls and Sgts all in line ahead of you for probably a single figure number of slots per year. And all the time you are waiting, your performance has to remain first class.
'Come back in a year' is definitely preferable to joining the ranks and working your way to a commission if you truly believe you are officer material. However, I know that Stellafella (sp!) has a different view and there are a few Mikes and Annalou (?) who may have a different perspective to offer?