Well, that depends totally on your budget. Basically the great difference between SSDs and HDDs is the storage capacity and the pricing. So if you're not bothered by either of those, just go ahead and get an SSD.
When talking about faster loading times the SSD basically blows away the HDD. So I haven't played GTA V that much but except for the initial loading of the game I don't remember it having that much and long in-game loading screens. As for Civ 5 - haven't played it, sorry. I was referring to games like Skyrim for example. You have loads of in-game loading screens - getting in and out of a house, fast travel, etc. But again, this is my point of view and doesn't necessarily mean that you won't like the boost for other types of games.
edit: Lol, seems like @guanyu has given the same example. But you get the idea for the type of games we are referring to. 😀