Of course for the majority of investigators this will be compared to Dr. Milan Christopher. She doesn't mix well Mark Harrigan and Zoey Samaras, but she works with the others just fine. Roland Banks, Joe Diamond and Leo Anderson have the options of taking either naturally, as does Carolyn Fern, but all the Dunwich investigators might consider this as well if their focus is a mixed bag or a desire for additional boost in their investigations.
With respect to the effect itself, Dr. Milan Christopher will be doing more work per turn given that he is not limited by the number of times that he can trigger in a single phase (although he probably should have been an exhaust just like Alice).
Alice is a secondary consideration in a larger group of investigators however where one of you can take Dr. Milan Christopher and the other can take Alice Luxley. She also has the capability of occasionally doing points of damage and combos well with Scene of the Crime that doesn't trigger attacks of opportunity. A nice, get a clue and swat that Will O' Wisp into a smear.
There are also secondary reasons to take Alice Luxley in addition to her effect of being able to increase offensive power. That one extra health might not seem like much, but the last two campaigns have been introducing treacheries that target allies with damage assigned to them. Alice Luxley can survive one of these being drawn, while Dr. Milan Christopher will be taken out. It's not as minor a thing as it might sound. Often, you will put down those one health allies to lose them halfway through a scenario, while Alice will remain for the entirety if you are lucky.