Hey Nodean, welcome to the forum!
All the guitars mentioned are great instruments but I'm a big, big fan of the Marsden so I'm a little bias!
A lot of the differences between the Marsden and 245 are cosmetic such as the neck binding. However, there are two key differences...
The Marsden has a 3 control layout of two volume and a master tone. I'm happy with that as all my guitars have had a 3 knob layout by pure coincidence. If you feel you really need two volumes and two tones that may rule it out for you. The other main difference is that the Marsden has a slightly larger neck than the 245 and just feels a little more comfortable than the 245 To me it made all the difference in the world but your mileage may vary.
For me the Marsden just looks fantastic with the quality of the tops they're using, the classic tuners and the binding. It'll handle the music you like without any issues whatsoever!
I've never tried the Tremonti but I have no doubt it's a fantastic instrument. I'd pimp for the Tremonti Custom over the older one perhaps.
So, my vote is for the Marsden but I'd really recommend trying them all out if you can and go with the one that speaks to you. I guarantee one will!
If you can't try the Marsden and Tremonti out then go with the 245 as you already know you love it!
One thing that is VERY important...
Pics once you've bought it!