This question is one that Jane and I have been looking into in some detail. There are many choices on offer and it can get very confusing.
The answer to this question has been posted on the OM4Tourism blog.
http://om4tourism.com/blog/liquid-inventory/
As it is quite a complex area, the article gives some background. But you can skip through to the section that looks at 5 questions you should assess before looking at 3 potential solution providers.