The most "bullet proof," and "brightest" I've seen are the 400W metal halide lights you might find in the ground around flagpoles.
Now, if your trees / shrubs are fairly small, and you only wish to light the area under the branches to, say, 4 ft. off the ground.... sort of accent the underbrush... then the low voltage garden lights with the 'glass mushroom' tops are hard to beat. The 'mushroom' diffuses the light, so you don't really see the fixture- yet the underside of the leaves is nicely lit woth a diffuse, soft light.
