For me, it depends more on the particular game than on the game system. For one-shot games, or those that will only last two or three sessions, I prefer random chargen. However, for any extended campaign I will only play with non-randomly-generated characters.
My bad luck with dice is nearly legendary, and playing a character nearly crippled by a single bad die roll (e.g. playing a 3e fighter who rolls under "2" for hit points for levels 2-5) for months and months on end is no fun at all.