The least likely to date would be a traditional floor. That is to say a 'natural' colour like oak or maple in a traditional plank (5 3/4" width) with a low grain level. If you want to work with a bit more of a "homey" feel without going out of style, a "knotty" presentation or something rustic in wide 7" plank is quite handsome.

Gray seems to be sticking around a little longer than many people anticipated. It looks fresh and modern NOW. This will make it easy to get quality renters (you can price the condo accordingly). In rental properties, it is the "norm" to have to change out flooring every 7 years....so in theory, the floor you put in now is probably NOT going to be the same floor in 7 years/when you go to sell it.

If you were living in the space and could take care of the laminate, you might fare better. Always assume a renter will reduce the life span of your flooring to 5-7 years. That way you know you can take steps to change out the flooring before putting it on the resale market.

Do you think I'm better off going with carpet on the second floor? I always thought laminate was quite durable and thought it would look nicer for a longer period of time than carpet.

I personally would be afraid to use laminate in a rental. It doesnt like water and you cannot trust people to treat it the way you expect! What about wood look tiles or vinyl?