There's no perfect answer - for some, it's a good idea to try the reserves first - Army life can be a shock to the system if your only prior exposure to the military has been Hollywood ...
Also - when I was in Recruiting, it broke my heart to see so many young recruits quit their jobs, put their stuff in storage, get a hero's send-off from their friends and family ... and then return home with their tail between their legs after failing/washing out ...
However, it's also true that the reserves aren't identical to the full-time Army - thus, some people might enjoy full-time more than part-time ... so, as I said - there's no perfect answer.
And so, the same advice I gave when I was in Recruiting was this:
If you would test drive a car before buying it, why not test drive your career (after all, a career lasts longer than a car ...).
And, the absolute best advice in the world is: Finish your education! (and, joining the reserves can help you achieve this)