WARNING: WALL OF TEXT INCOMING. TO AVOID BOREDOM, SKIP TO THE END.
Look at terrestrial fleets, once battleships ruled the waves but as soon as large weapons capable of taking one out from a small plane were launched, fighters rule the waves.
Looking at that piece of history we can safely predict the future in vague terms (nothing precise of course).
Let me put forward the most basic factors that influence any kind of combat.
-Terrain
-Weather
-Resources
-Desire/Will/Needs
-Technology
TERRAIN:
Be it on land, sea, air, or the vacuum of space, battles will always revolve around the terrain. It is the most important factor (IMO) since it dictate rules and boundaries that can not be broken.
WEATHER:
Anything in space that can affect combat and is constantly changing can be considered as "weather". Like for example a moving group of asteroids.
RESOURCES:
Resources are finite. The scope of the combat, the ability of man to engage in combat relies largely on the Resources which are available to do combat.
DESIRE/WILL/NEEDS:
This one should be easy, combat might not even occur if one side does not have the will to fight. One side might decide to retreat, if the desire for that thing they are fighting for is not enough to expend the resources needed to adquire/defend it. And if one side is in desperate need of that target, they will not refrain from doing whatever is necesary to obtain it.
TECHNOLOGY:
This go right after Resources, as it dictate the abilities and capabilities each side will posses.
Almost all arguments put forward in this thread have been presented after assuming a possible set of "values" for the factors presented here.
For example, Figthers. Arguments like "they are not worth it", "they are inefficient", "they are cheaper". They might be worth it and maybe even cheaper if the techonology allows it. They might be more efficient if the terran favors them.
Taking another history lesson, people though tanks were inefficient, until Germany showed the world how to use them. People thought small lightly armed fighter planes were not worth it until Pearl Harbor. People thought head on calvary and infantry charges were the best tactics until the charges were met with machine gun fire.
As we have only recently moved beyond our moon, we can not safely assume much about the Terrain and Weather of space's effect on manned space travel/combat. As we have not set foot on any other planet beside Earth, we can not assume much of the Resources we will find in space. As most people think of space as simply a new place for expensive recreational exploration(in other words, a money sink and play ground for nerds), we can not assume how our Desire/Need/Will will change when we learn more about space. And as our technology have been progressing almost exponentially in the last 100 years, we can not safely assume what technologys will exist in the next 100 years.
To end this wall of text, we simply can not say anything about space combat for certain at this time. REMEMBER, Necesity is the mother of all inventions. Right now, there is no necesity for space combat.