what is the most enticing offer???

well depends if you're a customer or hosting co.
if you're the company:
- 1/2 off FOREVER is ludicrious, you never know what may happen.
- 2nd free account? like forever? or just setup/1 mo?

if you're the customer, the one i'd pick would be domain name. the other ones look as if there's some catche or something.

caveat emptor

I'd say GOOD SUPPORT. Too bad that's not one of the options. Pricing or extras shouldn't be on the top of your list. A free domain name isn't so bad, depending on the plan, but half price off plans or free second hosting accounts just seems desperate. If they need to entice you with extras, they're probably not doing too well anyway.