A standard rule of thumb I use when writing chords symbols in most all types of music, that works 98, 99 percent of the time, barring certain exceptions, such as: certain 12 tone systems, clusters, pink and white noise, aleatoric, etc., is this:
I & IV = Maj7, 6/9, #11
ii, iii, iv = 7th or 9th (m11 mostly functions as a modified dominant or V7, a writing or notation preference.)
V7 = m7-5 or dim7, 9, 11, 13, # or b 5, 9 or 13.
Covers nearly everything logically, theoretically and easily readable.

Any unqualified 7 always = a b7, always. Chords larger than a 7 must conform to certain rules.
m7 must have at minimal a m3 and b7.
V7 must have at minimal a M3 and b7.

At minimal, this example, Fm13, can't be a minor 13th chord. Minimal chord tension would be b3, b7, 13. (Ab, Eb, D) This can't be anything but a tritone. In this case the tritone is more powerful than the Maj7, or my view, a mess or an affect or effect. And wouldn't notate in that manner.

[Edited by griphon2 on 11-11-2003 at 12:47 PM]