No, I myself began reading Toaru Majutsu no Index Manga and I say that you should begin reading the Light Novel, because it has every arc that was written by Kamachi(author of Toaru Majutsu no Index). The Index manga is, you can say, just an adaption from the Light Novel, but it skips 2 arcs that are somehow important(not so important like WWIII, but still important) and is behind the LN even more than the anime. If you don't like reading, I would recommend to watch the anime, because it covers a big part of the LN (there appear every arc, but some parts were taken out, but not so much that you won't understand, if you first watch the anime and then the LN). I would only recommend to read the Manga, if you can't imagine an object or something like that and don't want to search the part in the anime to find out, how it looks.
There exist only 2 LN about Railgun(It's just a spin-off series of Toaru Majutsu no Index, but still shows mostly the Science Side instead of the Magic Side). I would recommend to read the Railgun Manga, because the story was written orginally from Kamachi himself. The Anime is an adaption from the Manga, but it has filler arcs that don't appear in the Manga and messes the timeline.
There also exist an Accelerator Manga(a spin-off) and you can read it without any problems.
I would recommend to read the LN or at least watch the anime. Also, if you want to read Railgun, I would recommend to read the Manga and the LN. I wouldn't really recommend to read the Index Manga and the Railgun Anime, but if you want to read, I would recommend to read/watch it, after you have read/watch the former(Index LN/Anime, Railgun LN/Manga)
Sorry for my bad english