ICOs Pre-Mined vs. PoW vs. Poss

[VibENewS18]

What determines if an ICO does a presale, pre-mine, and further what determines if/why they choose PoW vs
 PoS?  I found Viberate doesn't have a Mining process but gives away their Altcoin/ERC20 Token for contributions.. Was this 100% Pre-Mined?

Info on Viberate:
https://blokt.com/icos/viberate-ico-review

https://themerkle.com/top-6-icos-which-sold-out-really-quickly/

http://www.financemagnates.com/thought-leadership/viberate-shakes-music-industry-vibe-token-crowdsale/