To be honest, very, very few realtors offer anything different. They all have access to the same listings and having an "unlisted" apartment is frowned upon in the industry. So majority of realtors offer nothing of value to differentiate from others except for their professionalism. You can always negotiate commissions but the rule of thumb is to never enter an agreement with someone who wants a lower commission. In all, just pick whoever you like the most because most don't so anything different.