Diner.
To OP. With a poll like this, consider that there are twice as many Taxi's as there are Diners so there are more people who own and have played and loved Taxi for that reason alone. That said, both games are great and this exact topic is often debated. I personally like diner more for these reasons: Diner call outs are awesome(taxi is great too but I like diner better). Diner rules I like better; it takes more effort to get through the characters and you maintain your progress. Coffee cup "hula hooping" is amazing, until you actually do this you wont understand. Also cash register repeated shots is fun. I like Taxi, but I don't think its as fun as Diner.