Short answer? Without a doubt! Do some searching in this forum...there are several threads asking this same question which already have very detailed answers and case studies to help you in your decision.
Yes Shaun but i think XF is decent about the many very young admins or unemployed people who have great creativity and skill but very little money. Some say it's too much and they have to save up. By making it cheap XF gets a more vibrant community - and sharp competition with its alternatives.
Have a good look in this section Sqirtle and check out the same question - it normally gets a big thorough answer but we're all overexcited because XF just won a huge court case that has dragged on for years.
In a quick sentence XF is fast, stable, SEO friendly, smooth on the admin side to operate and customise, has a vigorous addon community working closely with the core, - and fast support.
Love that name Squirtle - why not ask specific questions on what aspects of a forum are key for your project?
Depends on your requirements. If you are looking at Xenforo compared to the other paid options on the market, then yes. But if you need just a simple forum solution, it may be better to go with something like phpbb or another one of the free forum softwares.