Marker construction varies widely, from ultra-economy models not seriously made for the sport, to multi-thousand dollar electronic markers with custom graphics and body milling.
Marker body
The largest external and ergonomic difference in marker bodies is trigger and barrel position. High-end marker designers work to push the trigger frame forward toward the center, or slightly forward of center of the body. This allows the HPA tank to be mounted in a position that provides compactness and balance without requiring any additional modifications that drop the tank down and forward. (Such aftermarket "drop forwards," may create a large gun profile, which can cause eliminations due to hopper hits.) In economy markers, users often modify the marker to the extreme in this way, sacrificing a low profile to produce the same feel. Though this is an irrelevant consideration in games where equipment hits do not count, a majority of fields, even in woodsball games, will count hopper hits as an elimination. As a side note, some markers mount the barrel farther back in the gun body to preserve overall compactness.

Most electronic guns are built with light materials such as aluminum, plastic, or carbon fiber, to reduce the marker's weight.
Trigger frame
Triggers are the second external consideration, and one of the most important as it provides the player's direct interaction with the marker. Expensive markers universally employ electronic trigger frames with a variety of sensing methods. Some markers, especially autocockers, use carefully set pneumatics to achieve a light and short trigger pull. A good trigger will have an extremely short throw, with adjustable firing and travel limit stops.

Another important note is that valves and recocking mechanisms will have an effect on the minimum possible trigger travel. Electronic triggers may be straight switches, hall effect sensors, or break-beam IR tripped. Many markers are switching to magnetic trigger return, which provides decaying force as the trigger returns. The trigger frame is also what houses the logic for the rest of the marker, such as ball detection systems. Upgrades are available on most to improve the detection speed or increase customizability of the marker.
Valve
How the firing valve is designed to operate affects the recoil, rate of fire, and how the valve fires in time to the trigger pull. Many economic and rugged markers use a simple blowback design. Blowback guns require user-recocking when initially applying gas pressure. These valves are usually easy to replace and require little, if any, service work. The downside to this design, however, is its high operating pressure, which leads to a larger recoil and thus less accuracy. It can also send air back into the stack of paintballs, causing feed disruptions. Sear-trip or hammer systems use a hammer and spring valve, as in blowback guns, but do not use pressure from the valve to recock. A separate mechanism is present to operate the bolt motion. In a gun with electronic cocking, such as an upgraded Autococker, the hammer system remains in place while the cocking system is replaced with electronics. In an entirely electropneumatic marker, such as an Intimidator or E Matrix, both the bolt operation and valve operation are entirely electronic. Recocking the marker is no longer true recocking, as both the valve and bolt are operated electronically and on separate pneumatic systems.

Though most high-end tournament markers may be deemed "electropneumatic," there are various ways of operating the marker. The Matrix series and similar markers (Smart Parts Ion and Shocker, ICD Freestyle, FEP Quest and others) use a design called a spool valve; the Intimidator and similar markers (Planet Eclipse Ego, MacDev Cyborg, Bushmaster Series and many others) use a poppet valve design. The difference is the way the valve jets air. A spool uses a sliding seal where a poppet uses a face seal. Face seals have active force applied and the seal itself only experiences a compression force. A typical spool valve has at least 1 o-ring that undergoes a shear/compression duty cycle every shot, leading to faster wear and less reliability. However, due to having less reciprocating mass and requiring less pressure to operate, spool valve guns are well known for lack of kick, smooth operation, and very little noise.

Also, spool valves are usually fully balanced, meaning if the bolt was exposed it could be moved freely with your hand because there is no active force to overcome to vent the air. This problem has been largely overcome by the advent of better balanced valve designs. This has helped decrease the recoil while maintaining the wear and efficiency of the poppet design.

Most guns have a separate ultra-low pressure system that controls the gas pressure used to open and close the bolt. In totally electronic markers, kickback is almost entirely eliminated, as the only mass that must move in the gun is the bolt, which is often short. The firing valve will also open faster than is perceived by humans, giving a high end gun a distinct "fires before you pull the trigger" feel. Any marker with a hammer, such as the Tippman 98 and the Autococker, has a significant firing delay when compared to a full electropneumatic.

Valves also must be designed with a specific operating pressure in mind, but this can be altered to a large extent by changing the valve spring on most guns. Low pressure valves provide quieter operation, and increased gas efficiency when tuned properly. Going too low, just as too high, can decrease gas efficiency dramatically. The valve must let the proper amount of air through to prevent "shoot-down" and limiting rate of fire. Some guns have integral or external (or both) chambers, called expansion chambers, that hold a large volume of gas at the firing pressure directly attached to the valve. This prevents shoot-down and makes up for any lag in the regulator system. Shoot-down is not a serious problem in slower markers, but at 18-20 balls per second, how much gas a gun can continually stabilize and how fast it can do that becomes an issue.