I have done a bunch of research on the topic of 12 volt vs 5 volt pixels as this will obviously affect both what pixels I buy as well as which PSU (power supply units) I will need. Having said that, I sense it is all based on what you plan to do with them and how comfortable you feel with doing power injection. I even saw someone on a forum mention it is like the age old Ford vs Chevy discussion, which seems very appropriate.
From research I have gathered that 5v and 12v pixels are pretty much the same when it comes to what power they need to run properly. If they do not have enough power they will apparently look red or pink when you try to make them full white. Being colorblind, I may not notice if the pink is really light. I will have to depend on my family to point this out. Anyways, the pixels from both sets need around 5 volts to run at full white… but the 12v pixels use buck converters/resistors to step down the power. This would mean that power is being “wasted” and I suspect some level of heat is generated as a byproduct. The positive is that power loss over a lot of pixels/wire would be less of an impact for 12v given you have a lot of overhead to lose… where 5v dropping just a volt is not good for anyone.