There actually is a rule, called the 'Principle of Priority', which states that the nomenclature of a taxonomic group is based upon priority of publication hence option 2 in your question is the correct approach. In the principle III (Principle of Priority) section of the link above it is stated that
This principle states, in essence, that if a taxonomic group has been
given two or more names, the correct name is the first name that meets
the Code’s standards for publication.
But here the rule doesn't seem to apply....instead there is a piece of literature regarding the reclassification of gen. Vibrio to Campylobacter. In the paper "Neotype Strain for the Type Species,Campylobacter fetus (Smith and Taylor) Sebald and Vkon" (Veron & Chatelain, 1973) they state that:
A critical study of the present state of the classification of
vibrio-like, curved, microaerophilic bacteria was made. The species
originally described under the names Vibrio coli Doyle, V. jejuni
Jones et al., V. sputorum PrCvot, and V. bubulus Florent are
transferred to the genus Campylobacter Sebald and VCron
1963. The authors suggest that the type species of this genus, C. fetus, be divided into two subspecies: C. fetus subsp. fetus (Smith
and Taylor) comb. nov. (syn. V. fetus subsp. intestinalis Florent),
which contains the neotype strain of the species, and C. fetus subsp.
venerealis (Florent) comb. nov. The previously described subspecies V.
fetus subsp. intermedius Elazhari is regarded as an infrasubspecific
taxon with the name C. fetus subsp. venerealis biotype intermedius.
CIP 5396 (=ATCC 27374=NCTC 10842) is proposed as the neotype strain of
C. fetus subsp. fetus. This strain, then, is also the neotype strain
of C. fetus (Smith and Taylor) Sebald and Vkron.
The highlighted words suggest how they have approached in naming the species...