While it might take some work to mesh well with FTB, I'd like to suggest Custom Ore Generation. There is now a 162 version of it (last version was 147).
Potential issues to consider:
1. The default config - medium-sized veins - is fine for a normal overworld. If you want a UHS style map, you may want to configure them to smaller and/or less frequent.
2. Mod ores -- some mods add in ores in particular patterns already. Some use vanilla's WorldGenMinable. And then there's emeralds in vanilla's extreme hills. It is possible to substitute/replace very selectively, but the default config is either all or nothing. Note that to support mystcraft age features, you cannot just substitute everything. It should be possible to substitute emeralds in extreme hills, capture/redo mod ores that use WorldGenMinable, and leave special distributions unchanged; that's not a stock config.
3. Mystcraft ages -- since FTB includes mystcraft, do you want ages to look like the overworld, or be different from the overworld? (My own private server, we default ages to clouds instead of veins.)
4. Coal -- the default configs actually make you seriously short of natural coal because of the height generation (the veins basically do not spawn much in oceans, and the swamp bonus is roughly half lost.)