51. it rather depends on where you want to go with it! If you're looking magically themed, there are mods like EvilCraft and Astral Sorcery, and Roots 2 - those are all more complete in 1.12 though I believe. Likewise Embers (which is more magitech really). The 1.12 version of Botania has had a fairly big graphical change, much like Blood Magic did previously.
Otherwise, and I know this sounds odd, but I really recommend the Thermal suite! Thermal Expansion is really quite a different beastie than it was back in 1.7, I think you'd find lots of fun things to play with, and its very much being constantly updated. NuclearCraft sounds pretty interesting, though I haven't had chance to play with it.
Factory Tech adds in some really nice earlier game tech stuff that has a nice realistic feel to it.