The following assumes you wish to raid at a high end level at some point, aka Final Coil and whatever comes with Heavensward:

Bards are more necessary in a raid group than SMN, though both are desirable for their utility alone. It should be noted, assuming you don't already know this (which I suspect you do, but just to restate), that due to the nature of the Bards role in a group they generally won't be the highest dps out there and compared to summoner will generally do less. If you are a person who wants to push the numbers hard, but at least bring a good amount of utility (and I can't understate the importance of their battle rez and virus) then SMN is good. If you want to feel like the raid couldn't function without you, Bard is good. Just know you probably won't be pushing god levels of numbers.

The only problem with this is BRD tends to be a very popular class due to its accessibility (though it is very difficult to get "good" at) so you may find it harder to find a raid group as a BRD. SMNs are more rare (especially more so now that BLM just became Flavor of the Month among the casters due to the longevity of this raid tiers boss fights) but harder to get to a competent enough level to raid at a high end with. I hope this helps you make an informed decision, both are very good choices as both are extremely useful to any raid group, even in multiples.