To be fair with Scyther, its base stats and speed are still a good reason to keep it like that. Personally I think trades and babies that need friendship and aren't strong kinda break the novelty when meeting the mechanics.
I have trouble with Pokémon with trade evolutions, trade evolutions with certain items, and Pokémon that evolve in certain conditions (Friendship, time, etc.) I hate it when they do that...
Training a Larvitar all the way to become a Tyranitar is just brutal. Like, at least Dragonair is a decent Pokémon that you can have patience with, but Pupitar is basically another version of Metapod except it can actually use stuff other than Harden but it doesn't matter because Pupitar easily dies anyways which makes it a huge pain to level grind to level 55. @__@ Also trade evolutions. It's a real pain to find someone to trade with if you don't have friends that play Pokémon much.
The Deino and Larvesta lines for the sheer amount of grinding you have to do. Also, Porygons are a pain to get farming those upgrades and discs, but Mantine surf makes things easier I guess.
Also can I mention that, on the topic of trade evolutions, special mention to the Porygon line for being one of the most difficult to evolve Pokémon ever because finding the items to evolve it is just not easy. .-.
oh god uhh Chespin, Wartortle, Floette, Skiddo, Bunnelby come to mind. They're mons I adore and would love to use on my team if I didn't have to evolve them. And yeah....friendship evos are tough and are always the ones I never look forward to evolving, especially if they're Pokémon I want to have on my story team. Takes forever in older games without Protein/Carbos/etc spam. =s
I find any Pokémon that evolves through trading to be pretty much impossible. In order to do so I'd need to find someone else that I can trust to trade it to and then trade it back to me. I can (and do) get them from the GTS, but it's not the same as being able to use a Pokémon that I trained myself.
Pokémon that evolve with specific trade items were always hard for me because you only get like one of those items in-game. It's so rare, it's hard to give up because you never know what Pokémon would be the best with those items.
I would say Scyther, Scizor is cool and all but I prefer Scyther over it so I often don't evolve it when using one.