I prefer playing on my own, but sometimes I like having a partner. I tried playing an Ace computer and I beat it on my second try. I then played two Ace computers, but that took me around 30 attempts. Having a partner does help, but it can also put you at a disadvantage because you are more likely to mess up.
I haven't played MTO, but I'm guessing it can't be much different for the singles and doubles in the other games. But I always thought that doubles made it harder to score points, only due to having to pass two people that can hit it rather than 1.