I own nine Martins, all dreads. My oldest is the 1975 D-28 that I bought new nearly 40 years ago.
I have a 2002 D-28 Standard, a 2003 D-35 Standard, and a 2004 D-18 Standard.
I own a DC Aura, and a limited edition MTV-1. This guitar has Mahogany back and side on the treble side and the bass side is Rosewood. Very unusual, but it works.
I have a third -28, an HD-28V, for Vintage. This guitar has a Sitka top with the old-style forward-shifted bracing, RW backs and sides, and upgraded fretboard inlays. This guitar is tremendously dynamic and responsive. I have a strong voice and I can barely out-sing this one.
Finally, my last two acquisitions are -18s: A 2012 The D-18 and a D-18 Golden Era with a Shaded Top. The GE has the forward-shifted bracing of the HD-28V with Mahogany backs and sides, and this top is Adirondack. The neck is also wider (1-3/4")and deeper. Gorgeous guitar, again very responsive and loud.
The new D-18 is an amalgam of the Standard Series D-18, the D-18 Vintage, and the neck profile is taken from Martin's Performer Series--a new Taylor-esque profile and 1-3/4" width. It has a Sitka top with the forward-shifted bracing, making it very responsive and loud. The Standard and Vintage D-18s are discontinued. I think this guitar is killer--one of the best values in the Martin line. Its plain ornamentation appeals to many; it is a working man's guitar, and it should record very well. The Adi top of the GE model gives it a slightly crisper attack. Adi has the reputation of taking longer to break in and mellow out.
The HD-28 has an advantage over the standard D-28 in that it has scalloped bracing, but it is not forward-shifted as on the HD-28V. The sound is a bit tighter, and the bass is not quite as overpowering. I've attended Martin Clinics featuring renowned Nashville bluegrass picker and luthier Richard Starkey, who has an extensive collection of vintage Martins. He has told me that the HD-28 is in his opinion the most versatile Martin; if he could only own one, it would be the HD-28. I don't own an HD-28, but this makes sense to me.
The standard consensus for many years has been that if you are a male singer/songwriter strummer, a Rosewood dread like a D-28 is the way to go. And your buddy who plays the lead parts behind you should choose the cutting power of the Mahogany guitar. Doc and Merle Watson, Jim Croce and Maury, James Taylor and "Kootch", etc. Modern recording and PA system improvements make this a somewhat moot point.
But if you plug in, you should look a couple of other models in the Martin line. The new Retro Series offer the excellent Fishman F1 Aura pickup and preamp--this system is amazing. There are four models, a D-18, HD-28, D-45 and OM-28. These are just killer, and if I do wind up owning an HD-28, I suspect it will be a Retro model. The DC Aura that I have has an earlier version of Fishman's Aura system, and it works very well. These are built on Martin's -16 Series chassis with a mortise and tenon neck joint, rather than Martin's traditional dovetail. The neck on the DC Aura has a very low profile that will appeal to the electric guitarist. The bling factor of this guitar is nearly off the chart--lots of abalone.
And if you are a Taylor fan, Martin offers it's Performing Artist Series. The top line of these guitars is very impressive--a bit of Taylor feel and look, with warm Martin tone and soul.
I also have a 2002 Taylor 710CE with a Fishman preamp. Much better than the Expression System, but this guitar is not my favorite. It's getting very little use, as I prefer to play out with the DC Aura--it just sounds so much better. I'm probably going to sell the Taylor.
I hope this helps. Good luck in your tone journey. A Martin guitar is a lifelong friend. My old '75 has been with me through all the good times and the bad--one of the best investments I've ever made--not in the guitar...in ME.
Bill