Promo site - inside or outside?

It is necessary to make 1-2 pages of the promotion / competition for pr `attraction of attention.

And in this place, the question arose with my partners: how best to place such products?

1. on an existing company website, such as here www.visarussia.ru/promo/visafest_2005 or here - www.a4tech.info/promo/x7 ...?
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2. on a separate website with a separate domain, such as here - www.nf-hyundai.ru or here - www.sosedi.ru ...?

Who did what and how, and even if it doesn’t matter - who seems to be the most effective?