Can't go wrong either way, they're both great packs and not too far off from one another in price... I believe the Dakar HDs are about $150 less than the RXTs. OME has made a number of improvements to my newer leaf packs vs. the older ones I had on my last truck but the RXTs seem to be finished a little nicer in terms of paint. Both packs technically have three different levels of spring rate since you can add and remove leafs from both, the only difference is that the RXTs come with all three out of the box, the Dakars come in a "medium" or "heavy" and the additional spring for "extra heavy" has to be purchased separately. The RXTs are supposedly a bit more progressive as well but I've been really happy with the Dakars so it's truly a coin toss. You'd have to be running a shitload of weight to justify the 3rd leaf in either of the two packs.
I'm not sure what you plan on running for shocks, but both of these will flex like a boss so it would be wise to take advantage of that if you wheel a lot. If you go with the RXTs you could run Icon's RXT-specific rear shocks for a really nice combination, or pair the Dakars up with one of the custom or semi-custom shocks from someone like Headstrong, AccuTune or DSM. For budget minded shocks the Bilstein B110s also work well with the aftermarket leaf packs, but just remember that if you run any longer shocks you should plan on extending some wiring and running extended brake lines and diff breather line if you have relocated it. I'm currently in the process of sorting all that out on my new truck myself so you should definitely be aware of it in advance.