I like HA - I like it alot. It gives you some sort of safety net if you need it. If you have an encounter where you need a predictable SoTR Wall or have do endure strong physical damage for a longer peroid of time, HA is the way to go (doesnt matter if 10 or 25 man I would say).
However, DP should be used for everything else (or SW in 5.4, some discussion about that one in another thread recently). Mifuyne is right, most 13/13hc paladins use DP on farmcontent if they really don't need HA (I only use HA for DA HC Zerg in the current content). DP gives you theoretically a higher uptime of SoTR when you sim it.
From personal experience I can tell you, that especially if you have 4pt15, DP looks and feels superior. If you game DP correctly, you can have 15-20 secs of SoTR Wall without much trouble (at high haste values) given the right encounter. My longest DP proc chain was about 50 secs of SoTR Wall.
I used HA quite alot on HC Progression (Horridon, Megaera Solo Tank, Ji-Kun, DA, Iron Qon, Twins). Mostly because a) I needed a long SoTR Wall (3 Dogs + Qon) b) I needed a reliable Burst at a specific time + defense (megaera solo tank) or c) I just fitted quite nicely with tank switches / encounter design (ji-kun, horridon). For everything else I used - or should have used - DP. Sometimes I just didn't switch it out because I forgot or was too lazy.
Thing about HA is, it doesn't matter if you forget to switch it out. It performs quite well, no matter the encounter. If you forget to switch out DP on an encounter you really need HA for (like DA hc zerg), you're dead.
TL
R
You didn't mention your progression / experience. If you're in a "beginner-average" level, you're fine with HA. HA has the easierst learning curve and the best net result if you use it as another cooldown / it's more predictable. If you're at like 11/13 HC progression or something like that, you should really look at DP more closely.
Come 5.4 - especially if you plan on playing with Eternal Flame / 4pT16 - there is only DP. HA and SW are only niche abilities, depending on the boss fight. But DP should be the baseline.
Have a look at this thread:
http://www.mmo-champion.com/threads/...set?p=22250580
It has alot of discussion on HA/DP/SW and 5.4