Help much appreciated

I would like to know why is there different offensive units do they have different strengths are some cheaper than others, I would like to know

I would recommend looking at the documentation a lot is explained there.

Fighters, Bombers, and attack helis are great.
stealth bombers only attack military ground structures also great take few casualities
upgrade units a must at war level 2 or higher

Jose Luis, long time ago I learned from a veteran player, Aries, that air force units are better to attack than land forces; and he has reason, air force attack and bombing units (upgraded) destroys easily many targets, as mrp8196 suggest.

And as Alfonso says Fighters, Bombers, and attack helis are great.

Regards.

Thanks guys