Yes, it sounds like a strange but often important question. If not, I will probably not write this article.
Let's Begin. The question, as the title says, is to find out if we want to make a round trip with one airline or we prefer to go with one company and return with another company. Again, the answer is not clear but there are many things that can be said to give you a little guidance.
One might think that if you find a good price with an airline to go to but the return price is too high, efficiency will have a lower price. Well, it can be, but rarely. If you were on the day when prices with your outbound airline were high, then it might mean that efficiency will also have high prices on that day. The market is the same, and since higher prices are higher demand, it is strange that two airlines covering the same route on the same day have different demands, right?
Now with your approval, I will say this is not always like this, and the exception comes when we talk about awful timing flights. I call them that way because they really are. You need to wake up at 3:00 AM to arrive at the airport at 5:00 AM because your flight departs at 7:00 AM. Well, you may have found a good ticket here, in case the jurisdiction is not valid at the same time, of course!
A general rule also applies. Regardless of which route you choose, hot deals will almost always be for round trips, not for single trips. This puts you in trouble if you can find a good offer with another airline. If you travel with one company and return to another, you cannot get the deal but at the same time the price of return with the other airline has been very low! It is not easy, but if the airline has a good list of discount round trip travel deals, it is almost certainly the best option that you can make is those deals.
At the same time, flying with one airline will allow you to accumulate miles if you join a frequent flight program. If you go with one of them and return with the other, you will always end up getting points with all airlines but none of them will be refunded for anything because the quantity will not be high enough. In any case, the actual alliances make you able to change a few points from here to there, so you should think about that option as well.
After all, I would like to say that you usually find the best deal to fly with the same airline from all points of view, and I only recommend that you travel with another company in the event that the flight conditions provide you with clear advantages. In this case, keep in mind that you are sacrificing miles for a slightly better price, so think carefully before making a decision.