I agree with the above comments, although only one or two models usually apply to a given business (service versus distribution versus manufacturer). The best measure at any given time tends to be the latest sales (public and private) for companies in the same industry, with comparable size and EBITDA and similar client dynamics and growth rates (available from some data sources).
Company revenue, EBITDA and growth rates can have significant impact on the EBITDA multiple applied and ultimately the valuation. All things being equal, a 10MM top line with 2MM EBITDA will have a very different multiple applied to it than a 20MM with 4MM, or a 5MM with 1MM (although the EBITDA margin is the same, the larger company might have a 8X multiple while the smaller business a 5X multiple (e.g, 32MM valuation for the biggest guy and 5MM for the smallest although the bigger firm is only 4 times larger, they get 6.4 times the valuation).
We tend to use a discounted cash flow model to evaluate different businesses. Long term contracted client engagements along with repeat clients will up the value as you would suspect.
Ultimately, the true test is to have the business on the market and see what the market is willing to pay. Probably not practical but certainly the best measure. As a proxy, you can talk to some of the best investment bankers that handle your vertical and get a sense of what they understand the range of valuation... Good luck