While the guitar and the bass are certainly more similar than say the drums and a trumpet, the closer you inspect them, the more divergent they become.
Of course, there is the personality part of the equation, the jumping around the stage, windmill strumming and setting your guitar on fire of Eddie Van Halen, Pete Townshend and Jimi Hendrix versus the stoic, lurking in the shadows persona of John Entwistle, John Paul Jones and John Deacon.
I recommend you try and really analyze both guitar and bass parts in your favorite songs to see if one instrument speaks to you more than the other. Also watch some instructional videos by good teachers on YouTube to get a better sense of what each instrument is capable of.
A final consideration in favor of the bass is the fact that good bass players will always be in demand due to their limited supply.
For a more in-depth exploration of Guitar Vs Bass, see my 2-part series on the topic: part 1; part 2.