I really liked the TEKKIT mod back in the day, mostly because I liked going into outer space and onto the moon. I mostly found it through Markiplier's "Drunk Minecraft" series he was doing way back in the day. I also really love the Biomes O Plenty mod, because I love all the biomes it brings to the game, and I think it might even allow the Mojang developers that handle Minecraft and what type of biomes are added to the game, to implement more unique biomes that the mod showcases.