One of the best new features in Android Marshmallow is the ability to use your expandable storage to install games and apps on. You can actually use your external sdcards as normal internal storage. If you are going to use your external storage for games and apps you better be sure to purchase a high quality fast sdcard!
Today 32GB is the bare minimum I can recommend for a decent Android experience. Most Android phones use up about 6-10GB of your internal storage for the OS. If you start with 32GB you are left with 28-22GB. That may seem like plenty but if you use apps and store any media on your device even that will run out quickly, and if you have a 16GB phone you can forget about it. Luckily Amazon is having a super sale right now on sdcards. Now is the perfect time to stock up!
PNY High Performance microSD cards:
16GB - $9.98
32GB - $12.99
64GB - $24.99
128GB - $49.99
PNY Turbo Perfromance microSD cards:
16GB - $8.99
32GB - $14.99
64GB - $27.99
Samsung EVO microSD cards:
16GB - $8.99
32GB - $11.45
64GB - $21.99
128GB - $58.99