I don't know how it works with consoles, if you can pick your squads and all, but you can pick them and change them on PC. I will always go in and join the biggest squad with the highest ranking people I can. Not that it means they will be better, but you will generally get better play. Especially squad up with players with Veteran status. That pretty much guarantees a much better random grouping experience as well.
With consoles, all you get is a choice of whether you want to join a squad or not. If you choose "yes, put me in a squad," then the game assigns you to a squad. You can leave the squad you're assigned to and try to join another, but most of the time you get placed right back in the squad you left. Needless to say, this mechanic sucks. I know consoles are generally more limited than PCs, but you could choose your own squad in Killzone so I'm not sure why you're not allowed to in this game. Obviously you can squad up with people on your friends list.