I've been interested in composting for quite some time, but I have never actually had my own working compost pile. I made a valiant effort at our last place, but the steep slope in the backyard conquered me and I abandoned it. Of course, I have seen a design for sloped compost bin since then, but at the time I conceded defeat.
Now that we are flatlanders, I knew my dream of a compost pile would come true. I began researching composters, but the idea of vermicomposting kept popping up. I worked a little bit with both at Humboldt State, so I was definitely open to either. Here is a list of factors to consider when making this important decision:
Location
Worms work best at temperatures between 55 - 75 degrees Fahrenheit, so unless you plan on keeping them inside you might prefer an outdoor compost bin. If the temperature is too cold or too hot, the worms will die, so it isn't just a matter of efficiency. We couldn't even keep our bin in the garage because it gets so hot in there.
Nitrogen/Bedding
The dry component is important for both composting and vermicomposting. Food waste needs to be balanced out in order for efficient decomposition to occur. For a compost pile, this means leaves, dry grass clippings, paper and the like. I've even read that weeds are okay in a compost bin because the high temperatures will sterilize the seeds (though there is some disagreement on this). For a worm bin, leaves, cardboard and newspaper should work fine. With the worms I'm cautious about the chemicals I'm adding, so I wouldn't use bleached paper or anything with glue on it. Look around your house and decide what you would have available to add to your compost or worm bin.
Food Waste
This is the primary reason I was so interested in (vermi)composting. Fruit and vegetable waste, coffee grounds and tea leaves are great in both types of systems. You want to avoid meat, dairy, beans and fats in both compost piles and worm bins. However, a compost bin is a lot more forgiving so you can put in bread and other grains as well. Worms are more sensitive, so you should avoid proteins (gives them protein sores), and minimize citrus and onions. I also try not to put any unwashed produce that might have pesticides on it in my worm bin. The extra restrictions with worm bins may mean that you have a good amount of food waste left over, so be comfortable with that if you go the worm route.
End Product
Are you interested in compost or worm castings as a final result? Large amounts of compost are great in the garden, while smaller amounts of worm castings would be great in potted plants.
Cost
A compost pile can be fairly cheap, as you can just string up some chicken wire into a cylinder and call it day. You can make your own worm bin for under $5, but the redworms themselves are going to cost you around $30. Expensive composters and vermicomposting systems are available at a number of online stores as well.
Ick Factor
If you are easily grossed out, perhaps neither option will be for you. However, a low maintenance compost pile does not even require turning (though it will take a l-o-n-g time to produce finished compost), and piles are big enough that a shovel or pitchfork is usually used when you do turn it. Worm bins, on the other hand, require you to get in there with your hands, and you will touch squishy, wet, decaying food and slimy worms during the course of managing your worm bin. (This may not be true with the expensive worm tray systems though). Be realistic about what you are and are not willing to do.
Time
Composting doesn't have to be time-consuming. If you add to it one or two times a week and turn it once a week, your pile should be happy. There may be the occasional watering in the summer or covering up before the rain as well. A worm bin doesn't take much time either. You can add to it every couple of days depending on how many worms you have. I think the biggest time consumer is the bedding prep though. It takes some time to shred newspaper, collect leaves and cut up cardboard into smaller pieces. Some of this prep would be required for a compost pile too though.
Independence
You can leave your compost pile while you are on vacation without a worry or a care. However, can the same be said about your worms? You'll have to make sure they are well fed and have enough moisture in the bin before you leave, and if it is an extended trip you made need a worm-sitter to come by (though I have not left my little wormies alone that long yet, so I can't really say). Plus, it is going to hurt a lot more to say goodbye to those little Eisenia fetidas when you head out for the weekend then it would your compost pile. Or maybe I'm just a little too crazy about worms? Hmmm...
These are the major considerations that I used to help me decide which system would be right for me. I opted for a worm bin, which I will post about soon. However, after seeing so much of my food waste end up in the trash, I am thinking of starting a small compost pile too.