The rifles: Both the Winchester 94 (was 1894) and the Marlin 336 (was 36 was 1936 was 1893) are solid rifles. Their longevity alone almost proves that. There are some differences. One key difference is that the bolt on the Marlin can be easily removed to clean the rifle from the aft -- a task much harder with the Winchester.
If you want to mount a scope over the receiver, the Marlin does this more easily and naturally, even compared to the later angle-eject Win design.
If you want to shoot cast bullets, you might avoid the Marlins with the Micro-groove barrels, but there are plenty available with standard (Marlin calls it "Ballard") rifling. I believe that all Micro-groove barrels say so on the barrel, so you shouldn't have to guess.
My personal opinion is that in both cases the ones made before WW2 are better made and finished, and the 1950s examples are better than the 1960s and 70s ones. Older ones that were respectfully used may be smoother than new ones with fewer miles on the clock. The only ones that I'd positively avoid are the Win 94s made from 1964 to somewhere around 1970-72 that have a stamped cartridge lifter. Earlier ones were forged and machined, later ones were cast and machined. The stamped versions just rub me the wrong way.
I don't think I've ever seen a 94 or 336 that had been shot loose. I have seen bores that were pitted, rusted, or worn from sloppy cleaning from the muzzle. Other than that, I'd give the rifle a careful look-over. Do the screws look buggered? Might be evidence of unskilled tabletop gunsmithing. Are the sear and hammer worn? Can you bump, jar or push the hammer off the sear from full cock? Does the hammer fall if you press on the trigger at half cock? Again, check the bore carefully.
Receiver sights should be easy to mount. On the Marlin, and I believe (don't have one with me) on the Winchester, there will be two small diameter screws on the left rear of the receiver. These fill two holes for a receiver (peep) sight. I know that Marlin and Winchester were drilling and tapping these holes at least as far back as the 1950s; I'm not sure how much further back it goes. (Your next assignment is to find an old Lyman 66 receiver sight in steel, not the current aluminum that Lyman and Williams use...I am very down on aluminum receiver sights since dropping a rifle -- in a padded case -- loading the truck and having a Williams Foolproof sight made completely useless.) On the sight front, there are ribs that mount over the barrel and receiver -- at least for the Marlin 336/1895 rifles -- to allow you to attach a long eye relief scope "Scout" style. Not sure if they are made for the 94...on the Marlin, the rear of the rib attaches to the front scope mounting holes on the top of the receiver.
Safeties, what a nice hot button! These rifles were made for generations without cross-bolt or tang safeties and I don't think that anyone felt the designs were unsafe. Current Marlins all have cross-bolt safeties that seem almost guaranteed to do the wrong thing at the wrong time. The Winchesters had cross-bolt safeties that shared that fault and were, if anything, even more ugly than the Marlin version, but I believe they've been replaced with tang safeties. The tang safeties are at least less obvious cosmetically but don't necessarily contribute to safe or predictable handling. Someone is making kits for the Marlins that replace the cross-bolt safety with something that looks like an extra screw. As an alternative, you should be able to tighten a setscrew and lock the Marlin's safety in the disengaged position (something I would never recommend in a public forum that you do, because I don't want to blamed if doing so were to be connected to an injury or fatality with the modified rifle). None of these safeties does anything but lock the trigger, to my best recollection, so the rifle is not drop-safe and you need to religiously observe the Four (or Ten, or whatever version you learned) Commandments of gun safety.
Don't rush your purchase. There are literally millions of these rifles around in every conceiveable condition, configuration and age.
You didn't mention caliber, which is bait for another endless thread. Pistol caliber? Can get both makes in those calibers (the Marlin = 1894; Win makes their 1894 in pistol calibers, but there are also older 1892s in various pistol calibers). Rifles -- there are the standards, .30-30 (available in every rural hardware store in the US) and .32 Special (a great cartridge, but less easily available). Beyond that, the Marlins are reasonably available in .35 Remington, another great woods choice, and in .45-70 (the 1895). The Marlin is also still made in .444 Marlin, but I'll risk offending some here by saying I think the cartridge is handicapped by poor availability of bullets that are designed to perform well at the velocities developed by this cartridge (most bullets used in .444 loads are designed for good performance at handgun velocities). The Winchesters have been available in a variety of other cartridges over the years and if you go back before WW1 you can probably find all kinds of obsolete cartridges to consider (or ignore).
Yeow, time to end this and make room for someone else. Enjoy. Don't rush to purchase. Inpsect carefully and hold out for one that really appeals, because there is no shortage of good specimens of both.
and need all the help I can get.
