"Which phone should I buy?" depends on "What am I going to be using this phone for?" If you're going to play first person shooters, get the latest and greatest Samsung whatever. If you're going to use the phone to watch youtube videos, send text messages, catch up with the forum and what-not, follow the excellent advice posthuman gave in post #12.
One thing to consider: Some companies load their phones down with "bloatware," preinstalled programs that you can't remove, that you don't want. Some companies do NOT install a lot of bloatware. Lenovo is a good choice for a clean phone without a lot of junk preinstalled, and there are a few others.
Another thing to consider: Even the best company can have product line lemons. Research the exact model you're looking at, don't just go by "Oh this is a Moto phone, they're always good." Even my beloved Lenovo has a few products on the market that I wouldn't recommend. Usually googling the exact model and "review" will get you a good overview of how reliable that model is.