For example, we all know Le_Thien plays Diddy on an absurd level, but he still loses match-ups against people like RoyR.
Marth is very hard for sure, and even a great deal more irritating than Meta Knight in a few subtle ways, but I don't know how I feel about him being the most difficult match-up in the game. Personally, the Snake match-up has exponentially increased in headache and difficulty in recent months, as predominately campy styles of the character have been tearing me up lately.
DallasPhat of Dallas (LOL?) usually alternates between Marth and Meta Knight in tournaments, and although he's leveled up a great deal as a player since OH SNAP! v4.0, I don't usually lose to either of them at an alarming rate. However, after spending a couple of days with the Dallas scene over the past spring break, he is considering going Snake against me in tournament just because grenade-camping seemed to be so asininely effective against me. I didn't do much recording the first night I was at Bwett's apartment, so I'll have to see if I have footage of him crushing me for three or four matches straight by blowing **** up. =)
To date, Roy_R is still the only Marth I have ever lost a set to in tournament. In a similar vein, Dojo, M2K and Infinity on alternating months are the only Meta Knights who have occasionally demolished my will to play Brawl all together in friendlies. Other than that, I have not lost to a MK player in tournament since September. It would seem that my intense familiarity with both these match-ups have kept me afloat against your run-of-the-mill Marths and MKs, despite the advantages they hold in both respective match-ups.
And I'm just throwing this out there, but Roy_R is easily one of the Top 10 players in the country, and unquestionably the best Marth in this space-time continuum. No disrespect to NEO, who was one of the nicest and most impressive players I had the pleasure of meeting at CoT4.
Funny aside - I still haven't forgotten how I complained about a headache I was having during the first day of the tournament, and NEO asked DMBrandon to hook me up with ibuprofen while he was in the middle of a money match, LOL. Diem asked his girlfriend if it was in his bag, but he was out, so NEO asked OmegaBlackMage, who thankfully came through.