There are several types of gaslines available for your paintball marker, as listed below.
Stainless Steel Braided Hose:
This is probably the most popular type of gasline because it is the most reliable. It is obviously made of stainless steel braids, internally sealed with other means (polymers). SS Braided hoses come in finite lengths and are not disconnectable like macroline or microline (they come in lengths every inch or so). The best thing about the SS braided hose is that it is extremely reliable; they almost never leak. Pressure-wise, their fittings (at the ends) are rated to 1200-psi, however unless a malfunction occurs you'll never see that much pressure in your gun (only Automags would function above CO2 pressures anyway, however most preset regs don't even go that high). The downside to SS braided hoses is that once they're screwed onto your marker you cannot easily remove them without having to re-thread again. Threading involves applying some kind of thread sealant to prevent leaks, such as Locite or teflon tape, and sometimes is just a pain to do over and over. The other disadvantage is that they only come in a few lengths. SS braided hoses come on most low-end markers. The other disadvantage to this type of gasline is that it only comes in silver, so if you don't have a silver coloe scheme on your marker you mat not want it.
These will usually be seen on higher-end markers, but they will work on any kind (basically). Macroline involves two different pieces in order to work: two fittings for the ends and the actual hose that goes between them. The macroline hose itself is just a piece of plastic, unlike the braided hoses. The fittings are equipped with special crimp o-rings which seal around the macroline hose when inserted all the way into them. The correct way to install a macroline into a macroline fitting is to insert it all the way into the fitting then pull on it to seal the o-rings inside the fitting correctly. This means that you can quickly and easily disconnect and reconnect the macroline from its fittings, and is one of its main advantages. The other good thing about it is that in order to get the length you want all you have to do is cut the macroline to whatever exact length you desire. The bad thing about macroline is that it is somewhat prone to leaks because an exact seal must be created between the fittings and the hose. The fittings much be pulled taught in order to seal, and sometimes a corner in the hose will push down on a fitting and prevent it from sealing properly. The other sealing problem is that sometimes the fittings simply malfunction and need to be replaced, however some leaking problems are caused by scrapes on the surface of the macroline beneath the fittings, and thus can be solved by cutting half a centimeter off the end of the macroline. The last advantage over braided hose that macroline has is that it can come in colors (not just black). The actual pressure ratings of macroline varies from hose to hose but they average at about 900-psi (or perhaps a little higher).
This gasline is much similar to macroline however it uses a thinner hose made from a different material. Microline is the same small, flexible hose used on pneumatic regulators (such as the front end pneumatics on Autocockers or the LPR on an Impulse). Microline generally doesn't seal as high as macro, thus it is not usually recommended to be used with most markers. Even then, this does not mean microline is recommended with low pressure markers either. Microline uses a different fitting then macroline does.
High Pressure Hose:
This is a special black-colored hose seen occasionally. They seem to be quite different to find, as they are often mistaken for macroline. The difference is that these hoses are not disconnectable from their fittings and thus cannot be cut to any length. The advantage of them is that they are rated to 3000-psi. Many remote lines are made of this type of hose as a result.
Stainless Steel Hardline:
This is by far the most expensive gasline available. This is because it is difficult to make (each one is a custom job) and are expensive. These hoses are actual pieces of steel which are heated and bent to form corners, then are connected to small steel fittings. The downside of this is that it is relatively permanent. Don't expect to go out and simply make your own, though, because it requires many failures to get the technique right. And again, the materials needed are not cheap. Many of Doc Nickel's custom markers have harlines installed on them. Needless to say, stainless steel hardlines look extremely professional.