I tried scoping a couple of top-eject model 94's using a side-mount, and found them difficult to shoot with, very awkward. The other way to scope them is to mount a pistol scope forward of the receiver. Pricey, I'd imagine.
There's no real difference between the 30A and the 336, same action. Older 336 rifles have no pushbutton safety; they used a half-#### notch as did the Win 94. Both companies added crossbolt safeties in the 1980's, and sometime around 2000 or so Winchester went to a sliding tang safety. The half-#### is safe and dependable; I've owned a few of the Marlins and Winchesters and no problems. I never have owned one with a crossbolt safety and don't care to.
The Marlin 336 ejects from the side, is extremely easy to scope and is easy to remove the bolt from so that you may clean the bore from the breech. Most have a curved grip on the buttstock; this plus their extra 12 ounces or so of weight makes them not point quite as quickly and naturally as a Winchester 94, but that is seldom an issue. I would say that in general, though the rifles are built equally well, it's easier for the average person to shoot a Marlin accurately. Angle-eject Winchester 94's are also easy to scope, I should have mentioned. And I personally prefer the look of the Winchester. No reason for that.
I had sold all my .30-30's but inherited a 94 from my uncle last year. It's a lovely rifle and a great keepsake that I intend to hunt with a bit, and leave to a family member in my will.
That said, if I were looking for a rifle to actually seriously hunt with, that I might want to scope, I would get a Marlin, no question. I was foolish to sell the ones I had! That is unless I ran across a Winchester Angle Eject without a crossbolt safety at a good price; that would do as well.
There are debates in these forums all the time about how suitable the .30-30 is for moose/elk, but as a general-use cartridge, cheap, not much recoil, kill most game at reasonable range? It's a great rifle to have around!