I a on my second Sailfish. First was a 252, and now a 282. I debated whether I should move up to a Marlin, or stay with the Sailfish, and ended up very happily with the 282.
The questions you need to ask are:
Is the boat going to be moored full time, or do you plan on trailering the boat?
What emphasis is going to be on the cuddy size?
Is slightly different fuel consumption a factor?
How rough of water do you plan on consistently taking on?
Though the 300 is just 2 feet longer, in every aspect it is a significantly bigger boat. There is more room at every facet, from the cuddy, the mid berth, the helm area, and just a tad more in the cockpit. The Marlin rides better, and handles rougher water better.
For me, the Sailfish is the better all around boat as I choose to trailer it, and store it in a pole barn during the winter months. It tows very easy, and without a 2nd thought I can pull it out from her slip and move to another port to fish for a week if I want. I run charter tuna trips on my boat, and it fishes myself and 4 customers very well. Fuel economy for 150 mile round trip days is significantly better than my buddies that have Marlins. As far as rough water goes, the Sailfish is just slightly more crisp in chop than the Marlin.in 2-3 foot chop on top of a 5' swell, I can maintain basically the same speed as my pals with a Marlin. They push through a little more where I will bounce, but it is not too bad. I've spent many days on both, and the Marlin would be the boat I would get if I didn't have the trailering, fuel, and storage concerns.