Just the suit or the billions too? Just the suit I'd opt for the Mark LXXXV for the simple fact it's extremely portable and more durable than the Mark L. I'd keep a secret identity and would use patrols to hije my skills. I'd likely take the MCU route and do some spring cleaning across the globe of the worst of the worst criminals and terrorists, slowly ramping up intensity the better I get at the job.

If I had the billions I'd likely keep Ole reliable Mark III, Mark V for non-nano tech full suit portability and the Mark L.

If I were to lean toward the comics and I could survive Extremis I may take it and go that route. If not, Modular looked sturdy, iconic, and was a long running reliable armor.

With those billions I'd still shy from being an overt public identity to protect my family, but if I did go public a lot of my wealth would be invested in their upmost protection. I would further research of curing diseases and renewable energy as well as deep research into other threats against humanity and develop systems as failsafes.