JUST A GUESS :
From all conversations and research regarding (a)(12) and (c)(19), this is what I guessed. However, I might be wrong.

"Does not matter whether you put (a)(12) or (c)(19) on eligibility criteria. However, if you put (c)(19), they will issue your EAD as soon as possible even if your TPS application status is pending. If you are granted TPS, you have to renew your EAD with approved status which is (a)(12) category. In this situation you may need to pay extra amount to get the new EAD with approved TPS status.
If you put (a)(12), they don't issue an EAD until your TPS application(I-821) is approved".

Does it make sense guys? Please comment on this.

I second your understanding of this matter but we might be wrong.

Your posts just makes this confusion even worse...Just Put (C)(19) on your EAD application and wait no need to reapply your EAD for another 18 months which will be (A)(12) for re-registration...and you are welcome.

@ Satrianic, I am sorry. I did not mean that. I wanted to make sure so that we don't make mistake in filling the form and reduce the chance of rejection. I think, what you have said is the proper one. I HAVE DECIDED TO GO WITH (C)(19). CHEERS !!!

§ 244.5 Temporary treatment benefits
for eligible aliens.
(a) Prior to the registration period.
Prior to the registration period established
by DHS, a national of a foreign
state designated by DHS shall be afforded
temporary treatment benefits
upon the filing, after the effective date
of such designation, of a completed application
for Temporary Protected Status
which establishes the alien’s prima
facie eligibility for benefits under section
244 of the Act. This application
may be filed without fee. Temporary
treatment benefits, if granted, shall
terminate unless the registration fee is
paid or a waiver is sought within the
first thirty days of the registration period
designated by DHS. If the registration
fee is paid or a waiver is sought
within such thirty day period, temporary
treatment benefits shall continue
until terminated under §244.13.
The denial of temporary treatment
benefits prior to the registration period
designated by DHS shall be without
prejudice to the filing of an application
for Temporary Protected Status during
such registration period

C 19 would make sense if you had applied for EAD before TPS was granted.

what to put on part 2 no.4 since i have ead from past and all of them have same A# .and on i765 no 10 what should i put A# or i94 no.

http://www.uscis.gov/working-united-states/information-employers-employees/employer-information/employment-authorization
hope this helps

if you have TPS accepted, go with (a) 12