I have been an EMT for a year and when I start paramedic school in August it will be a year and two months. I volunteer about 5x a month on an emergency BLS rig and work full time on a BLS transport rig. Some people decide that they want to go straight into paramedic school after they complete EMT. Personally I am glad I waited. I have seen/had so much on the emergency BLS truck that has helped me as an EMT and I know will help me during paramedic school. Even on the transport truck I work on I have seen alot. It is neat to be able to be first on scene for an ALS call, do my assessment, O2, etc. just in time for ALS to get on scene and do their thing. I can give the information that I have gained from interviewing and doing my assessment to ALS when they get on scene and assist them with their advanced care. It is one thing to read about it and practice it in class...it is whole different story when you actually use it.
But it depends on different factors for different people. Some people prefer to "get it all over with"...maybe for financial reasons...or possibly because they feel the information will be "fresh on their mind". Best of luck.