That depends on whether you mean which one is easier to spawn or which one is easier to raise.
Bettas are easier to spawn IMO, far less picky about their environment and there's a lot more info on them out there. However, they are also far more aggressive and you need to consider the 'jarring' issue you'll be faced with as the fry mature (breeders of bettas 'jar' their fry - males only is necessary - to keep them from killing each other). This is all well if you have lots (as in 50+) of large half-gallon jars lying around and if you are prepaired to change the water in each of them every day - but it's far less convenient than raising the fry altogether like you would the dwarfs. Furthermore, (depending on where you live) it may be easier or more difficult to find homes for either species. With bettas, in the UK, few stores will sell them like they commonly do in the US in 'cups' and, therefor, it's difficult to offload large numbers on your LFS. Similarly, males of both species sell better than females. In the case of the dwarf gouramies, females are often not stocked by LFSs at all because their drab coloration provides for poorer sales. For both bettas and dwarf gouramies, the fry need to be raised on tiny live foods/liquid fry foods, which you need to make sure you have access to before attempting to breed them. Also, bettas need to be housed seperately from each other (and can be difficult to keep in a community set-up successfuly) while dwarf gouramies can be kept as a trio (1 male, 2 females) in a 20 gallon peaceful community tank quite comfortably. BUT, it's unlikely that you'll successfuly breed or raise any dwarf gouramies without providing a seperate 'breeding tank' and both they and the bettas would still require grow-out tanks for the older fry. Further consider that bettas often injure each other during spawning and that dwarf gouramies are highly susceptible to bacterial infections. Plus that getting hold of non-petshop (ie: not veiltail) bettas and female dwarfs can be tricky to say the least, sometimes quite expensive.
IMO, neither species is an ideal starting point if you've never bred gouramies before.
Three-spots (trichogaster trichopterus) are a better place to begin - but then only if you are willing to accomodate their somewhat cranky natures and larger size - as they are far easier to spawn, much more forgiving of mistakes and don't pose any issues as far as buying or selling them goes. The only downsides, as I've touched on, are their larger size (to 6") and aggressive nature (though not worse than bettas). If you aren't particularly interested in keeping them in a mixed-sex set-up, a group of females in a larger tank with community fish and a seperate 20 gallon for the male would resolve most aggression issues. A seperate tank would be necessary for the spawning to take place in/raising the fry. If you aren't looking to keep them in a community set-up, a 55 gallon contaning a single male and 4 or so females would also work - but any tankmates could be at risk if the male decides to go territorial/bubblenesting on them and a seperate fry tank will be necessary still.
Alternatively, my favourite gourami is the pearl (trichogaster leeri). The up-side here is that, whilst being almost as easy to breed as three-spots, they are far more peaceful. They do fine in mixed-sex groups (though 10 gallons per male, 5 gallons per female and more females than males is reccomended) and with other community fish. A seperate breeding tank is reccomended - and you'll need a grow-out tank regardless.
