I feel that this topic is one that comes up on every message board and every blog that even remotely deals with the 40k universe. Space marines are the mostprevalent army and the debate between their two main modes of transportation can get very heated.
Now on the 40k fan site 40k Online which I read frequently and on several other blogs I have purveyed, it seems to be that Rhinos are considered far and away the morecompetitive choice among the two.
Posters point to the reliable nature of the Rhino. The protection it gives the squad inside, along with the ability (barring it destruction/damage) to move your Space Marine troops around for the entirety of the battle. These factors push people to rate the Rhino ahead of the Drop Pod unless gamers are looking for something fun or fluffy.
I however look at the drop pod as being far and away more dynamic and game changing than the simple rhino. With its inertial guidance system it has all the benefits of deepstriking without nearly any of the draw backs. This means your troops will be nearly guaranteed to get to the objective you want them to.
But the true benefit in my mind is that you still get to benefit from the combat squadding rule for this drop podded squad. Where the rhino hopes to reach the objective with its full squad of 10 marines, or perhaps merely a 5 man tactical squad. The Drop pod lets you drop 2 five man marine squads in essence on the target. Not only does this let you target multiple enemies but it also means that the enemy has to destroy 2separate targets, and a third if the drop pod is close enough to contest as well, to clear the objective.
Surely Drop Pods do have their disadvantages. They involve certain callousness when thinking of your troops. Also they need to be committed to more fully than other transport options. I think a minimum of 3 if any, and 5 is nice for games past 1700pts. Its best in these situations to have your troop choices coming in the second wave of pods, or to have enough of them that it doesn't matter, because return fire and lost units is a big part of playing with drop pods. And a certain ammount of foresight will be necessary when opponents decide that they will
look like smug geniuses by simply leaving their army in reserve.
So you can keep your Rhinos you 40k pundits. But look to the skies because my pods are coming to rain fire and death.