I own a 2007 305 Express and my friend owns a 300 Marlin in the slip next to me here in Southern Maine.
I have fished and cruised on both boats.
My thoughts:
For fishing, the Marlin has its advantages. I bigger cockpit area is a plus and it is easier to get to the bow to help with anchoring.
On cold days, (There are many here in the Northeast) the ride to and from the fishing grounds is nicer on the 305 Express. We can fit 4 people in the helm area and can have conversations etc.
For cruising up to Casco Bay with wives and friends, my friend and I both like the 305 Express better. Again easier for the wives and family to have conversations and stay warm in the helm area.
Also, we find that due to the much bigger hard top on the 305 Express, there is much more shade on sunny days and I was able to mount 6 rod holders (4 in front of the life jacket net and 2 behind), keeping them out of the cabin.
The helm chair on my 305 Express does make it a tighter fit when walking around the helm area. When we are entertaining on the dock, I take out the helm chair, and I mount a large hand made wooden table (Which I store in the mid berth area when not in use) on the helm chair post. this serves as a great appetizer table and / or a place to put drinks or food etc. and it really opens up the helm area making it feel bigger and roomier.
Just my thoughts!
Both great boats.