So, I just registered on PBMining. I am thinking to buy 1 GH/s but.. it look like the minimum contract is 25 GH/s for 5 years. Please correct me if I'm wrong.
You can buy 1 Gh/s from AMHash for 0.0012 BTC. Like others have said though, that'll just get you dust.
If the goal is to spend less money upfront, then AMHash is a better deal than PBmining. If the goal is to have a higher long-term ROI, then PBmining is the better choice. Personally, I would rather have a higher ROI. 25GH/s in USD terms is under $15. Bitcoin is now over $400 (yay!!). As I mentioned before, if risking $15 on 25GH/s makes you uncomfortable, then Bitcoin mining is not for you.
***What are the payout differences between PBmining and AMHash? Let's assume we own 1TH/s: ***
PBmining: Looking at bitcoinwisdom.com/bitcoin/difficulty. Plug in 1TH/s, we would receive 0.08889BTC/week at current difficulty. Simple.
AMhash: The payout rate before fee subtraction is 25/ (difficulty * 4.295) BTC per unit per second. 1 unit = 1GH/s. So, the payout before fees for one week is ( 25 / ( 39,603,666,252 * 4.295 ) ) * 1000 units * (60*60*24*7 seconds) = 0.00000000014697 * 1000 * 604800 = 0.08888746BTC/week. That's pretty much exactly the same as PBmining. Then the maintenance fees must be subtracted from that amount.
The maintenance fee is 1.89*10^(-8) USD per unit per second or $0.01141 per GH per week. $0.01141 * 1000 units = $11.41 USD
The exchange rate is based on bitstamp.net 24h average. Let's assume the 24 hour average is $390. $11.41/$390 = 0.02925641BTC
The AMhash payout for a one week period is then 0.08888746 - 0.02925641 = 0.05963105BTC
***How much does it cost for 1TH, how often do I get paid, and what am I paid?***
PBmining: 1TH is currently 1.4BTC. Payouts are weekly. You receive 0.08889BTC/week at current difficulty.
AMhash: 1TH is currently 1.21BTC. Payouts are daily. The past 7 days of dividends have been 0.00000845 0.00000830 0.00000824 0.00000805 0.00000795 0.00000799 0.00000788 = 0.00005686BTC per unit for the week. 0.00005686 * 1000 = 0.05686BTC. This number is a little lower than 0.05963105BTC, because the value of a Bitcoin has risen over the past week.
***What's the better deal? PBmining or AMhash?***
The current upfront price difference for 1TH is that AMhash is 0.19BTC cheaper than PBmining. If the value of a Bitcoin is $390 USD for the next 8 weeks, then you will pay 0.02925641 * 8 = 0.23405128BTC in maintenance fees to AMhash, which negates any upfront savings and makes AMhash more expensive.
Unless you have a fear of long-term commitment, PBmining is by far the better deal.