I use both and have now built many sites and created Foundry & Foundation projects.
Your question about ease of use and speed is very easy to answer.
Ease of use: Generally, in Foundry, there are less settings and what settings there are, often don’t need altering because the default settings have been carefully chosen to look just right. Adams design flair is evident here. This means there is less tweaking with spacing in Foundry. There is good and thorough up to date documentation and RW7 based videos if you need it, all in one place. Overall, easier to use and has a shorter learning curve IMHO.
Speed: Foundry is noticeably faster in my experience, to Preview and use in Edit mode. A big contributor to this is I think that there are stacks such as Jumbotron or Banner which are just one single Foundry stack that would need many stacks inside stacks to create in Foundation. Also Foundry uses child stacks throughout which I am told speeds up Preview. Don’t be too concerned about less settings because Foundry is easy to adjust with a basic knowledge of CSS.
If you are coming from the Foundation world you will be blown away by some of the Foundry stacks but will miss the flexible form stacks, no image warehousing, some TopBar features and great 3rd party Foundation stacks. However, now that the Potion add-on pack is available this completely puts Foundry far ahead with many functions that Foundation can’t do without additional often expensive 3rd party stacks. Of course now there are plenty of free image warehouse solutions. In this respect Foundry + Potion is very rich in current design trend stacks whereas Foundation + Addon 1 & 2 feels dated and comes from the pre Hero 2014 world. This may or may not be important but compare the demo sites for both and make your own mind up.