In some ways this is a great problem to have. You both have living situations you like and feel happy with so the decision to move in together can be made from a place of want rather than from a place of need. Neither of you feels a strong need to escape from your living situation and it sounds like finances are not the driving issue behind the decision to move in together. Your satisfaction and independence provides a good foundation for making the decision to move in with each other.
Now to the hard part…who moves in with whom? Conventional psychological wisdom suggests that couples do best when they can create a fresh start by moving into a home together that is new to both of them. When you move into your partner’s home and leave yours behind, it is hard to shed the feeling that the home is really his, not both of yours. Naturally, this is true no matter in which direction the move occurs.
Of course, sometimes the decision to move into one house or the other is based on practical or economic necessity. Many couples can’t afford to finance a new home and are reluctant to sell their current property. Sometimes the houses they occupy are a much better value than anything you could find for a similar price in today’s market. So if you aren’t in a position to purchase a new home together, how can you make the decision of whole home to live in and how can you help the two of you feel that the house you share is truly both of yours?
Factors that may influence your decision include pets, the qualities and character of each of your neighborhoods, convenience to amenities (such as parks and shops), and whether one or the other of you would have a significantly longer commute as a result of a given move. One house may be larger and be a better fit for two (or more) people than the other house. Depending on the solidity of your commitment you may wish to consider selling one house, investing the proceeds in your partner’s house and having the house retitled in both of your names. However, this can be a daunting and complicated emotional and logistical challenge.
Short of this, a great deal can be accomplished by clearing out the interior of the house room by room and jointly redecorating it to reflect both of your interests, tastes and artistic inclinations. By creating a space that uniquely reflects the two of you as a couple you both symbolically and actually create a new, different and mutually created space to share. The one who is moving in may either sell or rent their home and the two of you can negotiate what expenses will be remain separate and which will be shared in the new joint household.
Most important, I encourage the two of you to move at a pace that allows each of you to adjust to the new, evolving living situation. While some people are ready to leap into complete togetherness and live together without a safety net, other mature adults who are very attached to the independence and security of having their own home may wish to ease into things more gradually. Try spending a week or a month primarily in the house you intend to live in and see how that feels to each of you. You can also try this in the other direction. One or both of you may be surprised at how your desires and comfort level shift when you have a chance to move in slowly and create a space that uniquely reflects you and your relationship.
There is no right or wrong way to do this and there is no single criterion that automatically makes moving one direction or the other the “best” thing to do. The right thing to do is what works for the two of you, both now and in the long-term picture of your relationship.