Beware its a folder, so a wide basket would stop you from folding it up like normal. I use a Topeak MX grocery basket for light loads on my bikes. Topeak makes heavier built smaller baskets too with the quick removal feature. I do need a smaller Topeak basket for the Portola.
I fold my Portola, so I like the easy to remove basket. Although I have been leaving a cheap but large rear bag on lately. If your short with the seat down low the big or tall baskets like mine hit you in the butt. I'll probably go back to Topeak rear bags on all of our bikes, I like the easy off and on track system.