Dominican Political Primer

Don't forget about the PRSC and Alianza Pais. 2 other parties who often get overlooked.

i think hillbilly's post in here sums it up pretty much (although i do not share his assessment of hipolito): http://www.dr1.com/forums/government/124001-please-explain-differences-major-political-parties.html
you get unsatisfactory answers because these are unsatisfactory political parties and ideological differences are hard to detect because dominican politics are not about ideology.
try asking one of the party militants why he supports his party and you will realize it is either about personal benefits, family tradition or, my favorite answer "because of juan bosch" "balaguer" or "pena gomez". balagueristas will point to the gifts he used to distribute back in the day, while morados and blancos will argue that their respective leaders were good men, most of the time without being able to specify which goals these men pursued.

My uncle voted for Balaguer because he approved his pension, his whole family (son's & daughters) became die-hard reformistas after that. My other uncle is a PRD man because he wants a government job & most of his friends are in it the party. My father loved Pena Gomez, since as a fellow blackman he admired his success. My father no longer favors the PRD as they have become a circus. I personally advocate and recommend Guillermo Moreno's Alianza Pais. As a result of the honesty and integrity of Lic. Moreno.
So ideology isn't really a factor.

the thing is, two major parties really aren't that much different. anecdotal reference giving a difference between PRD and PLD being nothing more that R and L is, somewhat, true.

PRD was founded in cuba, back in the times of trujillo, in 1939. one of the heads behind the program of the party was juan bosh. it was, esentially left-center party. socialist, not communist, because apparently, despite his cuban exile bosh was not a hard core communist himself, only swinging towards the left.
upon the demise of trujillo PRD arrived in the DR. bosh was already a popular politician and author and the following year he became a president of DR, albeit for a short time, before being overthrown by the military.

long story short PRD tried to gain back the power in 1965, american occupation followed and eventually they lost to balaguer and became, essentially an opposition party.
they got back into power in 1978 but in the meantime bosh became tired and dissapointed with the existing PRD program and left to start his own party, PLD, in 1973.

so, in essence, both PRD and PLD came from the same hands i suppose PLD was imagined by bosh as a better, upgraded version of PRD. think of it as PRD version beta. slightly more towards the center, i think. i really do not know how those two differ in terms of the political programs. the goals seem to be much the same: the progress and wellbeing of DR, if i may put it with such pathos. PRD is more popular among campesinos, PLD in big cities. i would go as far as to simplify their ruta to dominican success by saying thar PRD wants to achieve that by focusing on nature (agriculture, that is) and PLD by nurture (more modern ways, like industries and tourism).

the pld(danilo medina/leonel and the familia fernadez reyna are more like the democrates, socialist.more for government control and more a form of a dictorship.the prd are more like the republicans there for less taxes and more secured loans for business.captiolist.the want less taxes on business especially small business and farmers.less government.theres really not a group or party for poor or rich.poor people vote for both partys. its more for social issues.the problem that plaques this country is the corruption and the legality of paying people to vote for ur party.its amazing.its actually leagal.thats were it goes wrong for both partys and a true democratic process.in the dominican republic u can become president time,time over again.the only exception to this rule is that u can't rule consecutivly after 4 years.u have to wait 4 more years to run.amazing.