Plastic bases are ok but little else. Certainly, they have the advantage of coming with most of the miniatures, and hence that big plus of being FREE. If you're so inclined, you can decorate them with anything (flock, paint-on decorations, features modeled out of Green Stuff, 24K gold leaf if you don't like owning money). And if you want your units to rank or you play games with your miniatures, the square plastic bases are a must.

But for a more noble-looking base for a display piece within the budget of the average miniature painter (like me), I highly recommend wood.

Why wood?

It's Durable

Unless you're buying balsa wood, which can be used to make model airplanes but has no practical purpose in miniature basing, it can easily hold up to even pewter miniatures. Basswood in particular is light and durable, and is easily acquired from any hobby shop.

Comes in a Variety of Shapes

I'm speaking of the small or larger sized plaque pieces that come in the interesting shapes and sizes, usually used to mount a piece of brass that tells everyone how phenomenal the recipient is. For those that come unfinished (although you can buy the finished variety), you have a solid, well-shaped base that will mount a large pewter miniature with ease. Plus, it leaves plenty of space for any affectations you may wish to add onto the rest of it.

Again, I live within about 15 minutes from a craft store that sells these sorts of pieces in just the right sizes for a large miniature. They also sell them in sizes for small panoramas, so you can construct scenes or mount vehicles if you choose.

Alternative decoration

The big one. Wood that is thick enough to have sides can be decorated in multitude of ways not available with the simple plastic bases. While the details of each type are out of the scope of this article (as whole books have been and can be written about some of them), I list them here for those who may wish to pursue them in more depth.

Woodburning:

This is the art of basically "drawing" designs and shapes into wood with a burning tool. This leaves a burned-in design on the surfaces in which this is done, and with some practice, can produce beautiful results. I personally have only seen pictures of this sort of work and have no experience in doing this.

Woodcarving:

I actually have some real experience in this one. It's been a while since I've carved reliefs into wood, but this allows three-dimensional decorations to be placed on bases that can then be painted or stained (I mention staining below). If you want to learn or can already carve wood, you can really bat for the rafters and turn a wooden base into it's own work of art.

When carving wood, you face a tradeoff in the ease with which you can work it and the amount of smaller details it will hold. The hardwoods can hold lots of tiny details, but will take forever to shape and dull your tools quickly. Pine is a softer wood and carves with relative ease, but you won't be giving it much florid work. I've carved basswood without much trouble and had it hold all the details I wanted, but it's still a fairly soft and very dull-looking wood without a lot of visible grain.

Staining:

Unless you're working with a wood with no discernible grain, staining is a good choice. This will color the wood while letting the grain show through, which is a simple way to get a beautiful base quickly.

I've seen two forms of stains so far. The first is the liquid variety, which can be bought from a hardware store in any number of colorations. Most of them can be found in the smaller cans that aren't vastly more than you need (like the sizes used to stain entire deck porches or large pieces of furniture) and are inexpensive. They can be applied evenly with a rag, but can be a bit messy. It can also be smelly, so if you use this type, do so in a well-ventilated area.

The second is the gel variety. The gel version of which I'm speaking comes in a tube like paint. I have some of these is sizes of about two ounces (59 ml), which is more than enough for my purposes. It squeezes out in beads, which can be spread by a rag as above, but not as much of it is required. It's also neater, and far less smelly.

Either version will give you a beautifully stained base.

No priming required:

Not so important, but something to note. You don't have to prime wood to paint it. Paint will stick just as well either way.

In all other regards, wood can be decorated just like plastic, and the thicker pieces can be drilled, which means pinning is an option to help support your model and features. It can also be finished like plastic, so your wooden base can be a shiny, muted, or satiny wooden base if you like. So if you're ever looking to create a display piece rather than a table-grade miniature, wood basing is a good way to go.