The answer to this admittedly depends on the country you are registering from when hunting a bonus offer for new customers.
Specifically, a UK customer can expect to find the most attractive free bets or free enhanced odds on English Premier League fixtures. This also extends to UEFA Champions League and Europa League.
A typical match between Premier League heavyweights like Man City and Man United can turn out to be unbelievably rewarding if you make your first bet on a football event on them.
For example, you can deposit and stake £10 on a submarket that meets the minimum sports free bets odds requirement.