Trying to maximize efficiency between Warriors and Marauders is something that is almost a total waste of time. When you're comparing the two point-for-point, they're almost identical. 50 Marauders vs. 15-18 Warriors will hold up equally well against most foes.
That's where Marauders get their bonuses from having lots of ranks, which helps them stay Steadfast, but more importantly, helps them break Steadfast. The problem of course, is that most enemies who are Steadfast against Warriors (read, 3+ ranks) are the types of enemies you don't want to send the Marauders in against. Like 50 Goblins with Spears. That many attacks will leave your Marauders severely depleted, in a hurry.
Warriors do better against those Goblins, simply because they have the armor, WS, and Initiative to make sure that the Gobs hit the floor with as few returned casualties as possible. The Warriors will win combat, but they're going to have a hard time breaking the Goblins. Let's Hammer it out:
50 Gobs, Horded, Spears, vs. 50 GW MoK Marauders
Gobs go first
40A = 20 hits
20 Hits = 10 wounds
Marauders attack
40A = 20 hits
20 hits = 16 wounds
The Marauders are lucky to have 1 extra rank (they killed the whole back rank and reduced the 4th rank to 4 models), and thus win the combat by 7 and break Steadfast, but they sustained 20% casualties. A few more rounds of combat like that, or some shooting/magic on the way in, and those Marauders are going to be hurting, and a handful of Marauders isn't nearly as terrifying as a Horde.
Same Gob unit vs. 18 Warriors, MoK, Halbs
Warriors go first
24 attacks = 16 hits
16 hits = 13 wounds
Goblins turn
37 attacks = 18.5 hits
18.5 hits = 6 wounds
6 wounds = 3 failed armor saves
The Warriors win combat by 8 points (the Goblins still have a 4th rank, whereas the Warriors have 2 ranks +3 stragglers) but they don't break Steadfast. They only suffered 18% casualties however. This entire scenario was run assuming that Goblins are WS3 opponents (or substitute Empire Spearmen), at WS2, the Warriors take no casualties at all.
Warriors also hold up much better against most magic. Dwellers and any other Stat-check for the unit favors Warriors by far, and anything that grants an armor save and/or has a Strength value will obviously be more kind to the Warriors. Marauders are good when it comes to stuff that ignores armor (be it shooting, magic, or combat), although this isn't because they're better, it's just because there's more of them to soak up the damage.
This is also where the idea of damage-output vs. resilience comes into play. The Warriors are more resilient than the Maruaders, given that Goblin fight. You can imagine that the Warriors would last 6 rounds in that fight or similar combats before the last 3 of them were killed (even longer, since the number of Goblins will be dropping significantly over that time). Marauders can only make it 5 rounds in those conditions before they're wiped out. Worse yet, the Marauders combat output is spread over the entire unit - assuming 3 ranks attacking at once, with 2A in the front. Warriors focus their combat abilities on the front 2 ranks, and 75% of that damage is from the front rank alone. That's why most people will write off 15 Marauders charging at them, but they'll still worry a LOT about 6 Warriors.
Think about the roles you want your army to play. Warriors are great in combat, but have issues with Steadfast. Marauders are equally awesome in combat, provided they're not taking much damage... say, where do we see situations like that on the battlefield? Flank attacks. Marauders are excellent for running in and smashing the flanks of whatever your Warriors/Chosen/Knights/Trolls/Spawn/Uber-Lord is currently beating to a pulp. They provide enough ranks to reliably cancel enemy ranks, and enough bodies to cancel Steadfast as well, plus being able to spam enough damage to make most things just "disappear", and the flank of an enemy unit is generally a pretty safe place to attack.
But if you have Warriors who are wreaking carnage on the front of the fight, do you really need Marauders chewing through the flank like a buzz-saw? And how easy is it to get 50, 25mm bases into the flank of a combat? The answers are "not much" and "not very". So what if instead of 50, slobbering, crazy naked Marauders, we ran 30 (5x6 or 6x5) HW&S MoT Marauders as flankers? This unit is a good bit cheaper, has a 5+ parry save (because you'll rarely get the 6+ for your shield) and is still great at it's job. Furthermore, in a bind, they can still fulfill the "tarpit" roll. A 5+ Ward is equal to another 33% of your unit, so 30 Marauders actually looks a bit more like 40 when they're packing a Wardsave - not much of a trade is it?
There is one, final consideration. The more dice you're rolling, the better chance you have of rolling average. You also can't change your opponent's luck. With Marauders, you're banking on doing a lot of attacks, having them all hit, wound, and kill something - so you're praying you don't fluff your rolls. Then you're hoping that your opponent doesn't roll incredibly and take out TONS of Marauders (a real possibility with Ws4, T3, and no armor). If you lose 1 round of combat, you are left with 1A Marauders and a pretty low Leadership to test on. Warriors don't want to whiff their attacks either (face it, WoC is built on lucky attack rolls) but they have a lot more built in resilience - typically, to even hit a Warrior, the opponent has to roll higher-than-average.
In my lists, I run a full-plate battle line: 3 units of Warriors, two units of 15 Tzeentchians, and one unit of 18 MoKkers. I have Marauders in the list, 30 of them coming in with Wulfrik. When I do have them in the battle line, I put them at 6x5 and drop Festus into the unit in place of Wulfrik, for the 5+ regen. This makes them a bit more similar to Tzeentchian Marauders, and they work very well for me as flankers and the likes.