The custom I did the most was:
HCB+P, CC, HPx2, c.HPx2, HP -> QCF+LP xN -> finisher
This combo starter does slightly more damage with a much greater chance to whiff. You can also use HPx5 or 6, which does something like 150 more damage. Still not worth the chance of whiffing. I highly recommend the variation Gunter suggested.
Depending on where Todo is on screen, the finisher I use is diff. If in corner, I finish with grab -> combo. If midscreen, c.HK -> QCF,QCF+P (looks cool), or f+MK -> QCF,QCF+P (also looks cool, and moves you a bit closer to corner where the opponent will end up).
You also build up more stun on the opponents meter by doing the grab at the end. May or may not be worth it depending on how much you’ve hit them before the custom.
Against fatter chars (including Blanka), you can do grab (to finish custom), QCF+LP, MP -> QCF+LP, MP. This does 800 damage, and +44 stun. Against normal width chars, QCF+LP, MP -> QCF+LP does +33 stun.
What this means is, if you know how much stun you have inflicted before the custom, you can go for the easy dizzy. A typical grab -> QCF+LP, link low MK or stand MP will do 30-32 stun respectively. In many cases, opponents freeze up against the wave pressure when cornered, so it’s not uncommon to hop in after a low MK, or stand MP (which finishes the grab combo), and re-grab.
Using the grab at the end of the combo can be especially good against “lightweights” with only 60 stun points.
Anyway, it’s really up to you. 960 damage + no stun, or 700-800 (depending on width) +33-44 additional stun.
There are also other points to think about. Can your opponent wake-up with a DP (or do they have a super ready). If not, then finishing with the super, then tigerkneeing a wave (+300 guard damage and the advantage) can be an especially good choice.