The Dragons in general. Yes they are good, but no.. I gave up trying to raise a Flygon because I had no idea what to do with it.
Absol. Awesome design and Pressure is cool, but...It's not on my to-use list
Metagross. As much as I love Steven and Steel-types... it's hard to make it decent under my care.
Milotic. Cuz I don't want to waste time raising a Feebas - and I don't want to get a fully grown Milotic by trade.
Umbreon. Potential wasted under my care.
Ampharos. Same as above.