Well you can't juge a speaker by the frequency chart. Every speaker responses differently in different rooms. I know rooms where even the "best" speakers sound terrible. Your room and the speakers work together to create "that" sound.
Advice here is go to the store and ask if you can have both for a testdrive. Connect both. keep switching and listening
Hearing is believing
- Angelie
Obviously the room affects how different monitors will perform, and a decision shouldn't be made entirely based on the frequency chart. But for EDM, for example, where the low-end is arguably more important than in other genres, then a monitor with a frequency chart that shows a stronger low end response will probably (not definitely, but probably) be better than an equal-value monitor with a weak low end.
Also, while room affects monitors tremendously, it's likely that a shitty room will make both monitors sound worse, so even in a room with sub-optimal acoustics, I would take the Tannoy's over the M-Audios if they're at the same price point.
However, as Angelie said, hearing is believing. I prefer the sound of my $300 Ibanez acoustic over some $900 darker Martins, and with monitors it's no different. A lot of it is subjective, so to make a subjective decision it's best to take gear out for a test-drive.
In any case, I will say this: even if the monitors you decide to purchase aren't the best, you will eventually learn to adapt to your monitors and improve your mixes, regardless. Say, for example, you get cheap monitors that inaccurately reproduce the frequencies that you're mixing. After testing your mixes in the car, on a cd, in cheap computer speakers, etc, you will eventually know what to do from a mixing perspective, even if those very decisions are the OPPOSITE of what you should do on accurate, high-end monitors that properly reproduce the sounds.
Sorry for rambling but in short, when it comes to mixing, practicing is IMHO more important than starting off will all the higher end gear.
