Bitcoin mining PC
If you are going to mine with a PC. Do not by any means think you will mine bitcoin... You could make money on bitcoin with 2nd hand ASIC like Antminer S1 on ebay or something like that, but definitely not a PC.
If you wanna profit mining you can do many things, which I will explain later. First to answer the question.
To mine you will have 3 ways to move, you may choose multiple ways or a single route.
Way #1: CPU
CPU mining would depend on your amount of cores, and the speed. You would look into the CPU only algorithm to make sure you get profit. If you want the best efficiency I recommend a algorithim that is more new than Quark and supports CPU-Only architecture
Way #2: GPU:
GPU: If you want to mine with a GPU, I would definitely look into AMD. If you want specific, I find 2nd hand Cheap AMD GPUs like 7950 to get me ROI in about a month. If you want faster ROI and putting the GPU on a complete new computer, it would be much better to put about 3 GPUs or more so that the ROI is faster and more efficient. Use a algorithim like X11 or Scrypt-N. You will need to check the profitability and see the best coin profitability sites like CoinWarz. If you find it difficult, you can rent out your whole GPU(s) to a provider like where other people rent it and you can get a pretty decent rate. If you dont want to do that, a very profitable way would be investing in new coins that come up on in the Alternate Currency, Announcement board where you can see new coins, and mine them as there price could increase and u could just mine them when difficulty is low.
Way#3: HDD Capacity (not speed) - ONLY for Burst Coin
Just buy loads of cheap Hard Drives, even 2nd hand will be great :P Follow the Burst Guide, make sure to check if it is profitable or not and do the calculations with difficulty, and current price to see if it would be worth it