Traditionally :

The name of the bride always precedes the groom's name . In social importance, the woman is always first, then males, then children. Traditionally, the man's first and surnames are never separated.                                         

  Personal Preference: 

It seems the strict etiquette really applies mostly to the formal stationery, so for other items use your personal preference on what looks and ‘feels’ right to you.  Often times a couple is known to friends and family in a certain order and it feels funny to mix that up 

  What works for you:

It really comes down to you and your wishes, when designing a plaque we look at how the names layout over the surname and how well the letters and graphics balance and fit as a whole. Balance is the distribution of the visual weight of objects, colors, texture, and space. If the design was a scale, these elements should be balanced to make a design feel stable.  During the design process all of this is taken into account. When the design is complete a draft will be submitted to the customer for final approval before construction begins.