Pikachu doesn't have a spike. You can't clank a down b like other projectiles. Pikachu's projectile is terrible. That being said, pikachu is still top tier due to speed, grab, combos, priority, recovery, etc. It's my opinion that Samus is worst character material but isn't the worst character especially now that Hyrule is banned. Link is the worst character in my opinion and a case can be made that ness is worse than Samus. Just my opinion.
Best Pikachu vs. Samus match:
https://www.youtube.com/watch?v=zyACCwHndr0&list=FLHDuES2osaZNYehK7BXo16A&index=10
I would play the other smash games, but I'm too lazy to get a hold of the means to play them, am not going to spend money on them, and didn't grow up with the other games. I'm sure I'd get some entertainment out of them though (except Brawl I tried that once and felt like I was playing slow mo).
To answer the topic of the thread though, Link is good for beginners to learn z canceling and avoiding getting grabbed. Fox is good for combos and more advanced techs like SHDL and shining.