I think it depends a little bit on what field you intend to go into. If your interested in fields that will see a lot of elderly adults (I can't think of many fields that don't), you might want to have a book for reference.
I'm trying to make the same decision.... I'm looking at Essentials of Clinical Geriatrics, Current Geriatric Diagnosis & Treatment, Primary Care Geriatrics, or I may just stick with Geriatrics at your Fingertips (Given to me by the school). I'm working through Geriatrics at your Fingertips, to get an idea if its what I'm going to stick with.... and I'm thinking its probably good enough.
I'm thinking I'll go into primary care - and I have a feeling it'll be pretty important for me to learn how to treat geriatric patients and have some sort of reference book to look at later.