At todays prices, wearing out a writer by using it as an "everyday drive" is not the fright that it used to be.
One issue may be in the handling of protections (reading or writing, data or audio) - if the second drive can fill in for the things the first drive is weak on, that's better.
Having a "second opinion" on a DVD burn is also a good thing.
Given the current pricing though, theres not much to choose between:
DVD-ROM ... can be useful to have a non-writing drive that doesn't need ATIP-hiding if you use backups.
Combo or CD-RW ... essential if you want to use Mount Rainier CD-RW, since the support for that in DVD writers is practically nonexistent.
Another DVD Writer ... well, they cost no more than a CD-RW did not so long ago - the classic pairing would be a Liteon to scan, for an NEC that can't, but if the NEC scanning proves acceptable, the reasoning for that pairing rather disappears.