As the other answer mentioned it will take more memory to use but will be faster to render... that being said why not use a combination of both?
What I mean by that i sthat you could draw out the level using a very specific colour palette then when the level loads (or using a tool then saving the result) you could generate a map using the pixel colour of the full map as a guide for what tiles place in the actual game. So a green pixel could be grass, a grey one a road etc..
With a bit more logic you could place small variations of tiles so that the map looks better without having to do much more work or even create rules so that when a pixel is surrounded by X tiles of the same type it uses a different tile which is more related than the basic one. E.g. a basic tile could be short grass while a tile that is surrounded by 6 tile of the same type is long grass. It could also help make transitions between terrain types smoother (depending on what is required).