I voted Congo and had it longer then any pin in my current collection since April 2011. It's a very approachable pin for non pinhead guests and has some interesting shots. I know every new collector I have broken into the hobby really enjoyed it and was one of the top 3 after playing all my games. In fact last month I helped someone find Congo as their first game too and last year I helped another fella out too.
NGG is a very fun shooting game but I am not sure how I would enjoy it in long run in my collection. I can say for sure it has appeal because of the 'caddy shack-ish' type theme and the taunting gophers just make you wanna keep playing so you can bash them in their faces. The light show before multi-ball starting is one of the best.