AP -> QP -> solars is a 20:1 loss. Now that we have GCA (thanks Pokeboy!) you should be able to sell your QP for almost $1m :-)
However, you'll need VIP and a one time cash donation of $5 to transfer the QP (if you don't already have those).
Scatter/gather mining costs very little, pays little, and you're very vulnerable.
SOS (see Odlid's new, excellent guide
http://forum.astro-galaxy.com/index.php/topic,9989 ) pays very well, and scales nicely as you invest more in it.
PT (Prospector Treasure) mining pays well and scales nicely, but requires either SOS (to find PT's), or a marketplace for PTs. Investment is high, and diligence required is high as soon as the strength of your mods passes the 6-hr VIP auto-upload threshold (forget to click upload and your mod is soon clogged at 100% until the next auto-upload..)
COMs (especially when many are stacked on a single timer ship) pay even better, but require very high investment. However, they require very little diligence other than bookkeeping. Most high level players invest heavily or even exclusively in COMs for the convenience even more than the payout.