At what level should I start the various DLCs?

I've just downloaded LR and it mentioned that it was recommended for level 25 minimum characters.
I can't find any official figures for the levels at which you should start the other DLCs.

I've one character who's done all the DLCs and the main quest. He's at level 45 and I've started LR with by going back to a save before the Hoover Dam showdown.
It's been quite tough so far but I believe a lot of the enemies are levelled to match the player character.

I've a new character on the go playing hardcoe mode who hasn't done any DLCs yet, so when should I start?
I've read about people doing DLCs at level 1, but is this advisable?

I would guess that the entry level for each DLC should rise as you go along, as they've been released sequentially.

Officially, Dead Money recommend a level 20 character and Old World Blues recommend level 15. Honest Hearts doesn't have something like that, I don't think. But to be honest, I wouldn't recommend you do any DLC until you're at about level 30, not because they're that hard but because by that point, the enemies would drop some pretty rare weapons e.g. Brush guns, AMRs etc. You can end up farming a LOT of decent loot that way.

Just do OWB and LR at a low level. Enemies scale, scaled lobotomites and deathclaws arent fun. Did OWB at lvl 2, on vwery easy, becuase normal was insane.

Completely off topic... That vid on your sig was great!

I would do OWB at level 18, just enough that I am ABLE to pass all the speech checks and have perks enough to survive the nightstalker.