Unfortunately Lonely Planet really doesn't give you, in my opinion, a good idea of what to expect on the salt flats trip. But of course, we didn't do annnny research beforehand. So if you're reading this post, you're doing your research. Good for you.
There are two cities you can start from- Uyuni or Tupiza. For Tupiza, Lonely Planet recommends several companies. For Uyuni, they don't offer any suggestions since the market there is huge and always changing. Since we were already in Tupiza and wanted to head north afterward, we decided to look around. The primary reason why you have to do your research is because there have been several fatal accidents in the past 4 years. A good company will have experience, be able to show you a full menu, give you the complete run-down of all of the places you'll visit and not pressure you to book with them. Go with a company that gives you a good vibe, is honest and that has staff that is happy and able to answer all of your mundane questions.
We visited 3 companies, all on the Lonely Planet list. Valle Hermosa is just a few blocks from the bus station. They have 18 years of experience and lots of great recommendations posted on the walls around the office. The only thing was that they did "encourage" us quite a bit to leave a deposit, and we hadn't seen any other companies. They wanted to charge 1295 bolivianos. Tupiza Tours is "the first and the best," although the guide says they've gotten mixed reviews. The lady that explained everything to us was not smiley (you know how important that is for me) and wasn't eager to answer our questions. They were charging 1300 bolivianos.
The last company we visited was La Torre Tours. The lady that assisted us was friendly, and started off by telling us about the horrific accident that happened a few years ago where 2 tour vehicles crashed head on at full speed on the salt flats. (Tupiza Tours denied the occurrence of any major accidents). The lady at La Torre Tours also admitted having fired 2 of their drivers 3 years ago for drinking problems. Her honesty freaked out Carlos a bit but since I already had a vague idea of potential problems I welcomed her frankness. We decided to take a few hours to think on it.
Another thing you can do, besides researching online and reading my lovely posts, is talk to other travelers around town. Most people are willing to share their tips and opinions with you. Plus you might meet people you want to travel with. Remember, tour groups should be no bigger than 4 travelers, and 5 is pushing it. Plus the driver and cook. Trip vehicles are SUVs and they're top heavy, so if you have 6 people plus all of your luggage on top it can be dangerous. Ask for pictures of your vehicle and make sure what they give you is what they showed you. All drivers are supposed to be mechanics, too.
We decided to go with La Torre, after meeting several other groups that had done their research and were going with them. It's all about the good vibes. And here I am, writing this blog AFTER the trip, alive and well. La Torre is smaller than Tupiza Tours, but their drivers only work with them. The drivers also own their own vehicles. La Torre gives most of the $$ to the driver so he can pay the cook and gas, etc. The company provides employees with health insurance and other benefits. If they can't get a group of 4 together, the company pays the difference so that the driver still get his $$. The idea is that if customers are happy there will be more work and that the business should go well for everyone in the company.
We met participants along the way who were traveling with Tupiza Tours (several groups, actually) and Valle Hermosa. The general consensus is that all of the companies are great - responsible, good food and overall an enjoyable tour. We highly recommend going with a tour group from Tupiza if your travel plans are flexible. Upon arriving in Uyuni we met a group of travelers who had just been ripped off by a company that tried to fit 8 people into a truck. Plus all of the vehicles we saw didn't look as nice and new as ours (we had a Toyota Land Cruiser). And don't try to save a buck, it's not worth it. Any problems you have, make sure to speak directly with your driver or another group if you have safety concerns. No drugs, and your driver shouldn't be drinking at all. You probably shouldn't either too much with the altitude.
If you go with La Torre, ask for José and Augustina. They were responsible and sweet. Just be sure to shop around- pretend like you're looking for a doctor to perform heart surgery. It is that serious.