It is impossible to tell you which iron series is best for you based off the clubs you're currently playing. Titleist currently offers seven iron options. There are seven options because no one iron is the "best" for everyone. In order for you to get the best set of Titleist irons for your game, you should go through a fitting. It will help you identify which iron/shaft combo works best for you. If possible, go through your fitting outside. Hitting off of mats inside is okay, but an outside fitting is the best.

Forever is a long time. Without knowing where your game is today, we could guess anything from the T series.
There will be multiple responses to see an authorized Titleist fitter. There is a tab on the website for club fittings. You can start there if your regular course is not a Titleist fitter. Bonus if there is a Premier fitting site within reach of you.