S: Amazing. Likely to win tournaments. Very good MU spreads (worst MUs tend to be like 60-40, nothing worse). Have flaws, but can be easily worked around. Solo-mainable for sure.
A: Great. Likely for top 5, possible tournament winners. Tend to have certain flaws which, when exploited, can make it somewhat tough to win against other S / A tiers. Some may struggle from specific S / A MUs. Overall very strong though. Solo-mainable, can use a secondary for specific MUs.
B: Good. Potentially top 8, may take a tournament with a secondary or as a secondary to another top tier. Generally good MU spreads, but either have overall poor top tier MUs or have a couple of very, very bad MUs. Solo-mainable, but thrive when used alongside another character.
C: Really just an offshoot of B tier. I'd say these character either have less tournament representation, or have worse MUs than those in the tier above. Tend to need a secondary more than those in the tier above.
D: Ok. Likely for top 32. Characters have strong tools which allow them to outplay their opponent, but tend to have exploitable weaknesses or flaws which leave them vulnerable against certain characters. Usually have to outplay your opponent to win. Can use opponent's lack of MU knowledge to their advantage. Usually require secondary to make it to top 8 / 9th.
E: Flawed. Potentially top 32. Similar to D in that they have specific strong tool with exploitable weaknesses. However, these character's weaknesses either outnumber their flaws, or their flaws are so massive they find it difficult to preform. Basically require a secondary to make it to top 12, and can only get top 32 with great dedication / a skilled player to back them up. Lack of MU knowledge / skill on their opponent's behalf will usually assist in these char's bracket runs.
F: Avoid. Unlikely for any recognizable place. These characters have massive weaknesses which make them difficult to do well with. Either require and extremely skilled player behind them or bracket luck to make top 32. Tend to rely on the opponent's lack of MU knowledge or skill to secure wins.
Notes: No Miis because I've never fought any good ones. Also I tried to rank them in order, but the actual ranks themselves are much more important. Oh also assuming national tournaments for the rankings. Cloud is so new that idk where to put him really, so I may be under / overrating him.