Fine posts so far… here is some additional info… and my personal opinon: DECIMAL odds are what I use 
Depending on which markets the bookmaker targets, odds are presented by either the European (decimal), British (fractional) or American standard.
Please note, that when converting odds into the British standard, round-off errors may occur, since some odds don’t have an exact translation into British-style fractions. Here, we’ll show the nearest fractional odds.
Example: Brazil vs. England (Soccer)
| Europe | UK | US | |
| 1: Brazil | 1.40 | 2/5 | -250 |
| x: Draw | 3.75 | 11/4 | +275 |
| 2: England | 5.00 | 4/1 | +400 |
Calculations with the various odds formats are done with a stake of $200 on Brazil to win.
It is important to distinguish between the payout to your betting account after a win, and your winnings, which is the payout minus your stake.
European Odds (decimals)
European odds multiplied by your stake equals the payout. The odds show how many units the bookmaker pays out per unit staked.
Example: Home win to Brazil over England, Euro odds 1.40
| Payout: | Stake x Euro odds $200 x 1.40 |
= $280 |
| Winning: | Stake x (Euro odds – 1) $200 x (1.40 – 1) |
= $80 |
UK Odds (fractions)
UK odds multiplied with the your stake equals the winnings. The odds show how many units you win in pure winning per unit staked.
Example: Home win to Brazil over England, UK odds 2/5
| Payout: | Stake x (UK odds + 1) $200 x (2/5 +1) |
= $280 |
| Winning: | Stake x UK odds $200 x 2/5 |
= $80 |
US Odds
Negative Odds (necessary stake for a winning of 100 units):
Example: Home win to Brazil over England, US odds -250
| Payout: | Stake x (1 + 100/US odds) $200 x (1 + 100/250) |
= $280 |
| Winning: | Stake x 100/US odds $200 x 100/250 |
= $80 |
Notice that the negative sign in front of the odds is changed in the calculation. The number has to be positive.
Positive Odds (winning with a stake of 100 units):Example: Draw in Brazil vs. England, US odds +275
| Payout: | Stake x (1 + US odds/100) $200 x (1 + 275/100) |
= $750 |
| Winning: | Stake x US odds/100 $200 x 275/100 |
= $550 |
Cheers,
Rasmus