For me the difference isn't always huge (TAM was a waste), but i'm at a point in my life where I could afford business class for a treat anyway. I couldn't however afford (or at least justify to myself) First, so its nicer to do that as a treat, and bmi made that very easy through cash plus miles and generous earning.

The advice about choosing your carriers is very true, I've always been careful to avoid the American carriers as it is still a lot of extra miles and cash for not much more.

For me the difference is;
- More exclusive, so eight people (or so)whereas business has perhaps sixty.
- Lounges are superior and have nice twists, for example the spa in Bangkok for Thai.
- Wow factor, many people travel business, few travel first
- Better seat, and the chance of suites on certain routes which are really extra special
- Champagne and caviar, good quality and lots of them
- General improvements in service, but for the most part this is incremental over business.

But it's personal choice, and some carriers business is very nice anyway, particularly Air New Zealand.

I've probably spent close to 500K bmi miles (for two) in the last few years, and on first where possible (and will continue to do so)

And the most important reason... I travel perhaps a hundred times a year on business, almost all domestics in the UK, so it's nice to have a treat on holiday