You have to weigh the Pluses and minuses and come to your own decision. If we are comparing apples to apples, that is: Both in standard 20 inch configuration, here are my observations. Winchester 94- Pre 1964 models, very well made. if you can find one of the later post war guns in very good or better condition for a decent price get it! They have a smooth action and attention to detail was excellent as most parts were hand fitted at the factory by knowledgable gun builders. These are nice handy, smooth to slide in and out of a gun sleeve. The winchester 94 is 3/4 to 1 lb. lighter than the Marlin 336. The down side - I have never owned a win 94 that would shoot less than 3.5 inch groups at 100 yds. Pre world war ll guns have mostly seen alot of use, with many beeing worn out and have excessive headspace. A good condition pre-war working gun is going to be expensive. These are for the serious collectors.
Post '64 guns were poorly made because of less expensive parts and more automated assembly. I would not buy a winchester 94 between serial # 2,700,001 and 5,000,000. During the late 1980's and into the 90's, production quality did increase when the production was taken over by WRAC. IMHO production quality has since come down again (except fo the recent - Jap-Browning made ones) with the crossbolt and tang safety and rebounding hammers. I will not and do not own one of these guns. I was very fortunate a few yrs. back to pick up a very mildly used recent production .44 mag Saddle ring carbine (16 " barrel) that has the half cock (only) safety. I will keep that one untill my Son inherits it.
Marlin 36, 336 - Very well made carbine. The features that "marlin guys" really appreciate is the flat top reciever, round bolt, side eject and easy scope mount compatability. The Marlins in general will shoot groups 1/2 the size of Winchester 94 groups. I have one early 336 that I have shot 1" 3 shot groups at 100 yds. with, and this is a late 1940's production gun that looks pretty beat. I also have an early 1970's 336 in .35 remington that shoots 2.0" and under groups with its prefered ammo. Marlin did not Install cross bolt safeties into their carbines until 1983-1984. I don't like crossbolt safeties, so my Marlins are all pre-1983 models, except for a model 1894S carbine that I have in .41 Mag. My other son will inherit that one.
My favorite levergun- I have a Savage 99 H carbine in 30-30 that I will never part with. It was made in the early 1930's, excellent condition, and as smooth an action that you will ever find in a levergun. It is a great shooter, and groups nearly as good with iron sights as my Marlins do with scopes.
My vote is for the Savage 99.
If given a choice between a Marlin, Winchester, I would choose the Marlin as a serious hunting gun, and the winchester 94 as a casual camp or truck gun. A win SRC (16" barrel) would be my first choice in a self defense type of levergun.