How much you got to spend? $1 million, $10 million?
There are a lot of reports / articles on this subject. SBA publishes some good summaries from their clients. The most stable and profitable of the franchises is Subway. (One of the least is Quizmos, so it is not just a sector issue)
I use this service as one of many sources for your information request:
Industry Financial Ratios: financial ratios, industry ratios, industry balance sheet, industry profit & loss, industry financial analysis, financial benchmarks by BizMiner
Free Business Statistics, Financial Ratios and Industry Statistics by BizStats
RMA data from Library.
The Most Profitable Small Businesses - Forbes.com
Orthodontists (the wrecking yard of healthcare) is one of the more profitable of professional services... and to think they make a living on inflicting PAIN!!! Just think of the cash flows... They are largely private pay, they assure you PAY UP FRONT.
Anything with low barrier to entry and potential for 'e-commerce' erosion of clients / sales is a very BAD thing at the moment. You can't win by dropping prices.
Example #2.... Capital and carrying costs... (2 friends leave employment to start 2 businesses)
Friend (1) started an engineering service company... leased computers, contract employees, low overhead, cash up front from clients.
Friend (2) started a tool shop to support such businesses as #1 and other large companies... HIGH capital and overhead (employees and equipment). High taxes (personal property / B&O / L&I UI...) due to assets and risks required to support the business. Very long accounts receivables (90 days +). Very high carrying costs (projects take 6 months to complete). Very high Maint costs, very high insurance rates, very high utility rates.
Both businesses grow to 7 employees and plateau.
20 yrs later... company #1 has been sold 2x (owners retired early to start new firms) and employs ~ 100 people on 3 continents. Good health and growth.
Company #2 is very solid and has good reputation, but has had to lay off 3 employees, owner is back on the floor working, tax bills come every qtr for machines that sat idle during recession. Owner is happy but very tired. Machines are getting tired too. Employees are VERY hard to find (Since there is no (little) technical training and apprenticeships in last 15 yrs in USA.)
Next 20 yrs ??? you figure it out AND BE CAREFUL which business you buy.. Profit is not what it may seem.