So here are a few thoughts:
Topout spacers are the easiest to install, since you don't have to disassemble the strut. They also don't affect the ride, since the spring compression stays the same. However, they have two disadvantages if they provide more than about 2" or so of lift.
1) Up travel will now be limited by the shock compression rather than the bump stop. If you drive such that you frequently bottom the suspension hard, you'll likely bend and ultimately destroy the shock.
2) Down travel is extended, possibly to the point of binding up the inner CV joint at full droop, possibly leading to CV failure if you lift a wheel and apply full power. They can also cause over-angulation of the stock upper ball joint, which can ultimately destroy it.
Preload spacers avoid these issues, but they bias the suspension toward one end of its travel, such that you are more likely to hit the stops and get a rough ride. Plus, they are harder to install because you have to disassemble the strut.
The "combination" spacers attempt to balance out those issues at the cost of greater installation complexity. A 1" preload and a 1.5" top-out spacer is probably close to the optimum way to do a spacer lift. Keep in mind that these numbers are amount of lift. The actual spacer thicknesses will be about 1/2 of that because of the front suspension geometry.
If your offroading is "light", one of the combination versions should work well for you. If you plan to get into heavy duty offroading, you might eventually want to consider installing adjustable shocks such as the Bilstein 5100's (or more expensive and capable versions of the same thing.) Properly done, they eliminate most of the issues above.
I have a 2.5" top out spacer lift. I made very sure the CV's didn't bind, and I replaced the UCA's and upper ball joints with SPC UCA's for alignment purposes, so there are no UBJ issues. The result is I have a truck that rides great and works well on moderate trails. I am a very gentle offroader, however. No jumping or even driving fast.
