I find name combos that combine a more classic first name with an unexpected middle name stunning, e.g. [name_m]Andrew[/name_m] [name_m]Ignatius[/name_m] or [name_f]Emily[/name_f] [name_f]Cassiopeia[/name_f]. They always sound balanced and like you’re getting the best of both worlds out of your child’s name.
That said, the conclusion I’ve come to is that for myself, I gravitate more to uncommon first names. Barring a huge upheaval in taste, I suspect that’s how I’ll go. My question ultimately, is if you’ve decided on a less mainstream first name, would you pair it with something more “normal” for a middle name, or go for something different in the middle too? Any reason why? I’m looking for any and all opinions here, partially to help make up my own mind.
Thanks in advance! 
I prefer the balance of uncommon/unique and common, whether the uncommon name is first or second. I think if the uncommon name is in the middle, it gives an unexpected flair to a more common first name, like you said. If the uncommon name is in front and really grabs your attention, for good or bad, the more common middle name grounds it and keeps it from being too over the top.
I wouldn’t necessarily go with something common but instead with something familiar.
For example, [name_f]Cassiopeia[/name_f] [name_f]Margot[/name_f] and [name_m]Ignatius[/name_m] [name_m]Edgar[/name_m] feel just as balanced as [name_f]Cassiopeia[/name_f] [name_f]Emily[/name_f] and [name_m]Ignatius[/name_m] [name_m]Andrew[/name_m] while being a bit more interesting.
What I wouldn’t do is [name_f]Cassiopeia[/name_f] [name_f]Anthea[/name_f] or [name_m]Ignatius[/name_m] [name_u]Orion[/name_u] as [name_f]Anthea[/name_f] and [name_u]Orion[/name_u] are too unfamiliar to balance the first names out (if you want a balanced combo that is).
I would definitely balance it out a bit if that was my style. I tend to like names that are pretty mainstream but also classic. I used that style for both first and middle names for my own kids, but I still find their names quite balanced.
There is something about pairing popular (even wavering on the side of trendy) names with obscure names that I strongly dislike. Example: [name_u]Madison[/name_u] [name_f]Cornelia[/name_f] or [name_m]Augustus[/name_m] [name_u]Aidan[/name_u]. I think there is a fine line between balanced and unbalanced.
Thank you for your opinions so far.
With a rarer first, I don’t mind more unusual middles or more mainstream ones. I just go for whatever sounds or feels right. Usually there happens to be one more normal name in there, but that’s probably a coincidence, especially with two middles. I haven’t really thought about it when making combos, although I do like to make sure I have at least one more unusual middle with a more popular first.