In truth, one isn’t better than the other but there is certainly a trend emerging towards decimal odds. Historically fractional odds were used in the UK, especially on race tracks and on the highstreet. There are two key differences. Generally, decimal odds are easier to understand. Based on this, there has a movement to attract more people to horse racing by making it more accessible to the average punter. Ten years ago, if you were going to Cheltenham, all the odds would be displayed as fractional odds. Now, they’re largely all in decimals.
The second difference between the formats are that fractional odds only represent winnings, and do not include the returned stake compared to decimals which do include the stake. The transition from fractional odds to decimals largely kicked off with the growing popularity of the betting exchanges such Betfair. For odds to change slightly, it’s really difficult to marginally increase or decrease the probability without creating large fractions which are hard to compute for the punter.