There is a lot of discussion about the advantages and disadvantages of ways to capo the 5th string on a 5-string banjo. The two most popular ways are with a sliding capo, or model railroad spikes. The first question would be: what do I need either one for, and the second would be: is it really that big of a deal?
A capo is needed because the 5th string is a drone string, and sometimes it doesn't match the main chord of the song. For example, if you're in the key of D, the 5th string being a G won't be part of the main chord. When you play in D, you can either tune the 5th string down to F#, or up to A. The problem is most noticeable when the 5th string needs to be tuned to a relatively high note. It's easier and faster to use a capo, and the chances of the string breaking are reduced to zero. So, what's the answer? Railroad spikes are favored by many players because they don't protrude from the side of the neck, and the capo action is quick and easy. The down side is that the string can pop out of the spike and you have to drill a hole in the fingerboard. The sliding capo is also quick and easy, and depending on the brand of capo it can protrude to a fairly large degree (the spring loaded type), or very slightly (the Shubb capo). The biggest advantage of a sliding capo is that it can be used on any fret.  Most players who employ the railroad spikes have them installed at the 5th, 7th, 9th and sometimes 10th frets. The problem becomes acute when the song is in a key that would  need a capo at 6 or 8. With the spikes in the most popular positions, you'll still have to capo and then tune up or down a half step. The other argument I've heard is that the sliding capo requires that holes be drilled in the side of the neck which makes them harder to fill if you decide to remove the capo later. The spike holes can be filled and made to look like they almost never existed. The other argument against the sliding capo is that if you want to fret the 5th string, it can get in the way. If you have smaller hands this can be a problem, but the convenience of the sliding capo still outweighs the railroad spikes in my opinion. My best advice would be that if you buy a banjo that doesn't have a capo or spikes already installed, see if you can play one of each. If that's not possible I'd go for spikes first since the holes can be filled more easily. In the end it's more personal preference than anything, and the key point to remember is that your banjo should be equipped with what works best for you.