in all honestly its going to be a matter of preferences on most parts. but there is a few things you should pick first so it will determine your systems longevity
list of importants
1. Motherboard - i find this most important cause it determines everything that you will be using in your system. i5 or i7 will do very nicely
2 CPU - best bang for you buck has been i5 2500k from last i checked
3 GPU - prices are always constantly changing and no matter what everyone will be bias on this, I base most of my choice by tomshardware site they tend to be pretty good on there research http://www.tomshardware.com/reviews/...lock,3106.html
4.RAM - again there a dime a dozen out there just don't by some weird off brand crap. You can pick cards with lowest latency and stuff and pay higher prices but in all honestly you want notice that 1/10 of a second fastest while gaming
5. PSU - Any 80+ certified will do the big question is modular or not. And if your building and not on a budget definitely modular will save you frustration on the build
6. Hard drives - The can make a great deall of differences on load times specially ssd or raid 0 configs, but its storage so long as its a reliable it should be ok
7.Case- picking the right case can make it very easy to upgrade systems down they road. I prefer anything with a removable tray and rust filters learned for lesons of last build
8. Optional cooling- theres hundreds to choose from the big thing is what kind (water or air) and will it fit. This could be places above case choice chances are this item will be replaced again before anything else.

Part of the fun of build a case is pick the items yourself. If you want opinions between two items be more then glad help decide. But do the research on the tech pick what you think will best suit you