For me, personally (minority opinion incoming) ...
Marth ≥ Ike ≥ Roy > Lucina > Robin ^-^
Both Marth and Ike were buffed heavily since 3DS version launch.
Marth: I think that as the metagame becomes more and more defensive, characters who are able to safely space their attacks would benefit the most. Marth's traits could allow him to be very potent in this type of environment where proper spacing also leads to reward in extra damage; that tipper F-smash can easily end stocks sub-100%, especially with rage. The buff to Dolphin Slash makes it an even better OoS option, and the Jab buff improves his ground game considerably.
Ike: He has garnered more positive impressions from the community lately, even from the likes of ZeRo. Ike began as a rather sub-par character in the 3DS days and has since undergone major changes from the buff packages he received. The new vertical knockback trajectory on his D-tilt from 1.0.4. vastly improves his combo and follow-up ability; also from 1.0.4, F-air has a faster animation and gained auto-cancel properties. Ike's greatest boon, in my opinion, are his throw combos with D-throw and U-throw; both can true combo into Ike's aerials from low to mid percent. His U-throw combo would be further augmented by the next F-air buff in 1.0.8., which its hitbox was improved to hit above and below him better. Dash Attack was massively buffed as well, allowing it to finally kill. Landing lag reductions to four of his aerials and his Jab combo becoming more reliable were also pretty significant.
Roy: There was so much hype surrounding him during his announcement. As soon as players got their hands on him, many believe he would be the one to prevent "Fire Emblem Tier" from happening. I use Roy as a secondary, and I can say with much confidence that he is good. Blazer is an amazing OoS kill option, and he can be vicious with his low landing lag N-air and his ridiculous F-smash. His falling speed is fast, which complements his approaches and combos well; however, it can be hindrance to him if his opponents are able to exploit its weaknesses. Being a fast faller makes him susceptible to combos, and it most certainly does not help him off-stage as Blazer is already lacking as a vertical recovery. Additionally, he lacks SH auto-cancelled aerials, compared to his FE co-stars. I like to describe him as the most volatile character in the FE crew that reaps massive reward when used effectively.
Lucina: She received damage buffs to many of her attacks and was buffed similarly to Marth in 1.0.8. In the end, however, she would always be an afterthought to Marth as she lacks any sort of reward for proper spacing.
Robin: I want to say that this character's metagame is unexplored and that there is still some potential left, but until more Robins appear in tourneys, this will be my current placement for him/her. If I was ranking the FE characters several months ago, I probably would have said Robin was strongest, but the buffs that Marth, Ike, and Lucina have received were so substantial to their respective metagames that they all seemed to have passed him by.
tl;dr: I could imagine Marth, Ike, and Roy in the same tier together, with Lucina and Robin considerably far behind them.