We stayed at the Platon appartments near the Panoramic Hotel. The up side is the quiet location with easy access to Argostoli 20 minute walk / £3 taxi ride. Lassi is further away than you expect 35-40 mins (which is no bad thing if you don't like the typical brits-abroad holiday resort experience). Gerry who runs the place is a great source of information about the island, its history, what to do etc, and is fanatical about keeping his pool clean.
The down side was the lack of a sea & sunset view (only some appartments have this, though there is a comunal terrace at the front of the appartment block). The dogs next door barking through the night and in the early morning. The self catering arrangements were pretty poor; I mean you expect basic, but that shouldn't mean filthy cutlery and crockery... And the cleaning arrangements were not perfect.
Your own transport is an absolute MUST! as is a good guide book or you might miss out on some of the sights of the island. Don't go to Kefalonia if you are expecting wild nightlife, the 'top' nightclub being the Cinema club which would be funny if the drinks weren't £5 each... But for great food, history, and BEAUTIFUL scenery it is perfect!