I'm a big fan of free walking tours. I think it is a great way to discover the cities and that is affordable for everybody because you can tip according to your financial situation.
Sandemans was the first company whom with I did a Free walking tour (10 years ago), and I have discover different cities with them.
They are good, interesting and you leave the city feeling more of its magic, which is something that I personally really enjoy. Also, the tour guides are usually really friendly and willing to give you all the advices they can.
The problem is that Sandemans offers other tours which are payed, so they spend half an hour talking about them, and then they give you a 20 minute break, which really consists of a time to get you to buy them. This frustrates me because they last the same as other companies, but around 50 minutes are only dedicated to the commercialization of their other tours, instead of in stories or information of the city. This makes me feel like I'm not discovering the city as much as I could, and it makes me want to book with other companies instead, because I feel like I’m getting more from them in the same amount of time and price ☹