"Two and a half hours" sounds more natural, in my opinion. The other is right but I hear (and use) "two and a half hours" way more frequently.

"Two and a half hours" is correct. I've never heard anyone say "two hours and a half". It sounds very archaic. If an English speaker said that, I would think maybe that person is from England or somewhere in the UK because I've never heard it used in America.

I agree with Bennett. Note that there was a popular American TV show called "Two and Half Men." http://www.tvguide.com/tvshows/two-and-a-half-men/100558

Both are correct. Everyone is different, but I would say the second when I'm angry, and the first when talking casually. "I can't believe the Dr made me wait for Two and a Half hours!" and "I was only there for about two hours and a half"

'Two hours and a half' is *not* considered correct in English - some English speakers may say it but that does not mean it is correct. In general, we prefer to keep units and fractions together: two and a half metres (not two metres and a half); two and a half years (not two years and a half), two and a half men (not two men and a half), etc. The only common exception is for one and a fraction, but only if we substitute the number (one) for an indefinite article (a/an): we may say 'one and a half hours' OR 'an hour and a half'; one and a half miles OR a mile and a half (etc.). We would not say *one* hour and a half because it sounds weird, breaking the rule of keeping units and fractions together. It forces us to consider the unit to be one hour (singular) instead of more than one hour (plural: hours), which is incorrect because 1.5 > 1 (obviously). This does not happen when substituting the number for an article, and it is also the reason for only applying it to one and a fraction, and not to two (or higher) and a fraction.