DM if your speech skill is at least 60%.
HH otherwise.
I would say not, since you have a better idea of how to do what you need to do, and where some important things are.
It's still tough though, the cloud and the speakers see to that.
Talking to all the NPCs helps a lot, they can give advice and teach you valuable skills.
If you're waiting until Level 20 to start I'd say Old World Blues especially if you're playing a Energy Weapons character. The mobs in that zone get a lot tougher if you wait until higher levels. Honest Hearts has a bit of the same problem but it's a bit more manageable.
Honest Hearts and Old World Blues I've both completed after going in at Level 1 but the weapons you get and the levels you earn will make a lot of the Mojave trivial and boring as a result. Personally I try and get Honest Hearts done around Level 12-15 so long as I can raise speech to 90 for the best "good guy" ending. Followed close behind by OWB (all though waiting until you have Medicine and Science into the 70's will give you a lot more dialog options). Lonesome Road, if I bother with it, about 35-40. Dead Money I've tried a few times but never bothered to finish it. I just don't care for the gameplay, environment or characters.
They are actually all pretty doable on low level because the enemies scale and are easily killable - Dead Money is pretty fun on low level but you can't take some shortcuts if you don'T have decent lockpick and/or science skill. But on level 20 I recommend to do them in order (HH, DM, OWB, LR).
Thanks for the info guys I just finished HH I'm going to OWB with SPeech guns energy lockpick at 100 so far I'm gonna do DM third because I disliked it as my lvl 50 character last time I played it
i always recommen hitting LR early in the game just for the mass of easy caps you can make, then without even finishing Ashton you leave and use all the money you get rom the commisary to buy you a GRA weapon and easily walk through HH or OWB