
How is this ally better than Dr. M? While it does not seem fair towards other allies, it is only reasonable to ask this question. So how is Whitton Greene better? Can she, in fact, be better?
Whitton's +1 is conditional, but depending on your deck, the condition doesn't need to be that harsh. Plus she actively works on fulfilling the condition!
While Milan gives you pretty reliably a coin every turn, Whitton does something completely different. She finds your books, she finds your relics, she triggers deck searches, thinning your deck so you can draw other important stuff earlier. All this is very synergical with the cardpool. Milan makes you rich, Whitton makes you stronger and faster.
If you have upgraded the Dream Diary, you want to draw it as soon as you can. Milan doesn't help with that. If you are planning to assemble the Pendant of the Queen, it is Whitton who finds you the pieces. Plus it is reasonable to expect her to trigger an Astounding Revelation or two and give you some money so you don't miss Milan that much.
Whitton's impact only increases with lower player count. But even in larger groups, you can find a way to trigger her enough times to find all the stuff you need.
Picking Milan is rarely a bad choice. But we shouldn't be lazy and do it automatically, because other allies may be just the same help, sometimes even bigger.