they have some of the hand poisitions of each but to say the best of both worlds? hardly, if you like flat bars and you like riding on the top of the hoods of road brakes then bullhorns have everything you want, but you still lack a few positions of drops, i have atleast 6 different positions i use in my drops, i rode nitto rb021 bullhorns for years(and loved them) but i only had 5 hand positions, flats offer one, pretty much any bar attached to your stem will offer all the advantages of a flat bar(aside from aesthetics), obviously it's different bars for different riders/ types of riding but between drops and a flat bar i say go with the drops,

the lack of numbness in your hands the first time you ride over ten miles will be proof you went the right direction