I'm probably going to personally use BoP for these main reasons.
One: Its biomes are more pleasing to me than EBXL or any other biome adder
Two: It has the most integration from other mods that I've seen
Three: It adds useful things like mud, cattails, berries, and the sickle.
Four: I know I can basically kill the number of biomes it generates or use the loonium from botania (in conjunction with TooMuchLoot removing a lot of the complete and utter junk. I really want apples stored in a box in a moss-covered dungeon that is infested with undead and/or spiders... yuck) to get biome essences for the Biome radar. Which also fixes an issue I have in even vanilla worlds. I have had seeds that I can't find Extreme Hills, or Desert, or Swamp, or an Icy biome for like... 10 klicks in any direction! Which if you're doing a reasonably efficient search means you're generating over a million chunks... which is a really big world on the hard drive (I've done some pretty large worlds with things like Minecraft Land Generator and Admin Control Toolbox. Worlds even a fraction of this size take up gigabytes)
It will likely be neutered to have a tiny handful of my favorite biomes, and just enough to reasonably balance out the gem (and thereby biome) distribution (hopefully via CoG). Wonder if there's a mod that lets me muck with biome tagging... hmm.
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I've had nothing but trouble from mods that unduly muck with the world generator; ATG for example, it looks awesome but it kills biome distribution... and every world I tried looked the same. It was basically a volcanic island chain world. Large dormant shield volcanic islands with some sort of forest on them adrift in a ****ing giant sea.
I tried millienare like... ages ago. Back when IndustrialCraft was basically the only mod for minecraft that wasn't "here's a new kind of sword/pick", in the Beta days. Jeez that seems like centuries ago now. Minecraft, you are not allowed to make me feel old. The custom NPC's mod looks like it'll be great though. I don't intend on ever releasing the pack and I'll easily be able to restrain myself from making my "citizens" into Ye Olde Flying Brick (that would be Superman's basic set of superhero powers for those not in the know of the lingo) or Marty Stu (overpowered author's pet character). Can I (having never played with the mod before) make them do some of the things from... oh blast I can't recall any of the mods now. Basically can I make a farmer work like 1.8 villager farmers do? Or a lumberjack that actually goes and plants trees in random locales I designate as "forest"? So that not only are they not horrifically derpy squidwards, but they can also make my world slightly dynamic?
Honestly I'll probably just generate and re-generate worlds until I spawn in a decent valley-type location near a forest (source of wood) with a village and icy biome less than a klick (kilometer, 1.6 miles, a thousand blocks) from spawn (which I will likely move a bit if the world's chosen spawn is derpy) thereby providing me an area to let my capital expand into, as well as resources that I won't have to truck for miles back to base
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Ok, Vazkii is awesome. There's been an update to Botania, and it added something called "trodden dirt", which then linked to a reddit post for credit of inspiration and texture. Which had a bunch of links in it, some as ideas, some as bukkit plugins... and one as a Command Block "module".
I'm so going to implement that in my R2R world!