Smartest place to keep my money?

[Johnny Thompson]

Hello, I'm looking for some advice on my situation as a 28 year old. My real estate goal is to buy enough cash flowing rental properties to retire early and I should need about 10-12 to reach this goal. My short term goal is to save up $100k to have some capital to work with and piece of mind. I currently have 2 SFRs. 

I'm a W2 employee that makes good money. I take the full 6% company match on my 401k but nothing more. I have employee stock program that I contribute 4% to that lets me purchase stock twice a year at a 15% discount of the lowest stock price in the previous 6 months. 

As I am working towards my saving goal, should I also be maxing out a Roth IRA or SDIRA? Or should I just keep that money in a savings account to purchase my next properties? Any advice would be appreciated.