It's all in the character compatibility. Key to that is rescue dating, so your piggy can decide under expert supervision who they get on with and want to be friends with. You come home with a new companion only after acceptance has happened (speed dating) or after the rough bit of the bonding has happened (residential/boarding bonding). With one of our recommended good welfare standard rescues you can also be assured that any piggy has been fully quarantined/vet cared is properly sexed and guaranteed to not pregnant. Good rescues know the personalities of their piggies and are experienced with bonding, so they can see pretty quickly whether a match is promising or not. Adult boars past teenage have a much smaller fall out rate; theirs is comparable to that of sows by then.
Cross gender bondings have the least fall-out rate but there are two major obstacles: the neutering operation (there are no or hardly ever any spayed sows in rescues) and initial acceptance from the sow/sows, which is by no means a given. Especially not with any adult sows! Again, mutual liking and compatible personalities are crucial; and again, rescue dating is the safest way to find a match.
Otherwise you will have to have a plan B for any piggy you are bringing home on spec in case the bonding fails.
There is no one way is better - it very much depends on your rescue and vet access. We have lots of members with very happily boar pairs and others with cross gender or sow pairs. I've had one very happy boar bond (Nosgan didn't vibe with sows) and have several sow bonds that are not interested in boars in addition to my mixed gender pairs and groups.
Sometimes it has taken quite a while to find a suitable partner. I am back there again with my Beryn (a human orientated dumped ex-single) after the only piggy she ever accepted sadly passed away unexpected in February.... But she is my most extreme case.
