hello. Welcome to cruise-chat.
I didn't look to see if either ship has been refurbished yet. Since they are in the same class of ship, I personally would let itinerary decide. I would think the price difference would not be enough to consider that factor. If the itinerary are similar enough, you state "they have just about the same things to offer", what are the differences. I imagine the price is pretty much the same. I would choose itinerary/ports over price and ship, in my opinion. I have been on the explorer, not the mariner. I would guess the mariner is wonderful, as was the explorer. Good luck
There is always the use of a travel agent to help you all decide. Lil' Lori