Most programs request three letters of recommendation (although more are allowable, it is typically not helpful to load down your application with extraneous LORs). So, who should you choose? The most common solution is to submit two letters from neurologists and one from anyone else you think would supply you with a strong recommendation.
In the past, some residency programs required a letter from the chair of the neurology department at the applicant's medical school. While this is no longer mandatory, many applicants feel that a chair's letter greatly strengthens their application, so you may wish to ask your chair for a letter. This is more or less thought of as part of a chair's job, so don't feel like you are imposing too greatly. It is also common to request a letter from the attending you had the best relationship with during your neurology clerkship.
No matter who you choose, be prepared. Bring a CV, a transcript, and the latest draft of your personal statement to your meeting with the letter writer (and schedule an appointment, don't just try to catch them after rounds). You should give your writers at least a month, preferably more, to work on your letter.