I agree with
hectorm that quarter-dome buttons with a relief device are well suited to a rugged blazer that proclaims its nautical pedigree firmly.
It seems to me that otherwise, the choice should be influenced by the cloth (as
hectorm notes), the expected occasions for wearing, and the affiliations and whimsy of the wearer.
For my own part, I've always valued the advice John Kent gave me regarding dressier blazers, especially if SB—which was that plain flat shanked polished gold or gold-filled buttons of moderate size are always correct and understated, as plain gold oval cufflinks are always correct; that otherwise said buttons engraved or embossed with the device of one's club, hunt, service branch or regiment, etc. are acceptable. I'd extend this to silver as well. Things like school or college buttons, etc. would be appropriate for relevant occasions.
For my own part I'd never wear personal monograms, or devices derived from ranks or organizations I don't inhabit, but others may be happy to do so. Whimsical devices to taste.
My preference is plain gold, until and unless I find an engraver and funding to hand engrave one of my organizational devices. Here's an example of the kind of engraving I mean, though a bit more extensive and whimsical than I'd want, on an 18th-century set of silver hunt buttons:
Benson and Clegg will do custom engraving on gilt buttons, but it appears from the uniform line that the cutting is done by machine or laser. Here's an example, showing an armorial crest:
