I like a good balance of all, but in person is definitely my preferred. I feel like the latter two are better for some light teasing or later on in the story when the couple decides to experiment even further, so they can send each other pictures of their adventures and/or talk about it once they are reunited in person again, to spice up their night or morning for some good sex/lovemaking.
I feel like in person stuff being the focus, with the other elements there to elevate their desires even more and to make some hot 1-on-1 scenes by adding spice to their intimate moments, is probably the best for me. However, as long as the MC isn't a doormat/submissive or being humiliated, and as long as it's all consensual and nothing is behind the others back and it doesn't turn into NTR, then I'm fine with it all, no matter which it focuses on.
Also, I wouldn't consider it being behind the back if the couple decides on an open relationship to a degree with certain boundaries/rules set in place obviously. I'm not of the mind that you need to ask every single time you meet someone you want to fool around with as long as you tell your partner afterwards and it was an agreed to arrangement before hand, I.E. the couple had a conversation about their boundaries when they were first figuring out the lifestyle (Or maybe at a later point once they've figured out the direction they want to take things after experimenting) and decide they want to open up the relationship and discuss what it would entail and what rules/boundaries to set in place. Like always telling each other, taking pictures/video for each other, using protection or birth control, and any number or combination of different things.
Regardless of it being only swinging or a combination of swinging and an open relationship, as long as it isn't NTR and the couple communicates and respects the others feelings and boundaries (and of course no doormat like previously mentioned), then I'm down for just about anything, as long as it's interesting and well written. I'm tired of the Engrish games lately, it would be a breath of fresh air to play a game in the genre with good English for a change.
I'm completely on board with this being an option, as long as there's an option to join in sometimes too. I think variety in setups, and options are always a plus. Also, I definitely prefer broader swinging games to stag/vixen (and especially cuck, which I'm not a fan of) focused games, but I enjoy both as long as they're done well.