I tried to use the ZAM soul calculator buts its kinda wonky right now for some reason so I didn't do it. I"m running Pally Reaver Warlord.
14 Points in Reaver for AOE: DOTS / Heals etc. To help hold aggro and mitigate damage
16 Points in Warlord for extra armor / dodge and a pull skill. Also it would have only been 15 but the warlord has the skill "Imposing" which causes extra threat and incoming attacks to generate threat. This helps survivability / threat generation.
The rest are in Pally because of the block and block related skills as well as (later in the tree) good threat generation and decent AOE. As well as the fact that it does the highest damage, in my opinion.
Basically in any given encounter I spam my reaver macro which is Plague bringer->Soul Sickness->Necrotic Wounds which will get most mobs to immediately attack me. If there are more than 5 mobs I will also drop the pally skill Judgement to pick up the stragglers. If that doesn't do it I have the pally skills Shield Charge and Shield throw as well as the Warlord skill Sergeant's Order all of which will force single targets to attack me for 3 seconds, long enough to steal aggro.
I can also use the Lights Decree pally skill to spread individual attack damage up to 5 additional enemies helping hold aggro.
Then I'll start spamming my pally macro. I don't remember the specific order but it consists of: Pacifying strike (the instant Last in the macro), Retaliation, Disarming counterblow, Face Slam, and finally Aggressive Block. This macro ensures that my block activated attacks always hit as soon as they are available. In addition this macro will boost block , generate threat, interrupt casting, and give me some damage mitigation.
Finally throw in the Paladin's Reprisal skill and the warlord macro (buff armor and decreases enemy chance to hit)and all the remaining miscellaneous skills.
From my experience (used this build from level 25 up) I can tank anything, no problems.
All in all the extra heals really don't matter much to me because the Warlord DOTS and the Pally macro both heal me a percentage of the damage they do. I also have the Venomous Faestone Essence (i'm trying to figure out if there is a lvl 50 equivalent) that pretty frequently heals me for 375.
All in all Single enemy tanking (assuming the healer is dead) I can stay at 99% health for quite a while. Then if I get to less than 10% health I drop the paladin full heal for Full health.
All in all I started googling "rift tank builds" to see if there was anything better, and I don't really thing there is. However, this is an all purpose tank. I also have a 51 VoidKnight, a 51 paladin, and a 51 Reaver, for specific occaisons where their unique abilities are required.
(like in RD there the final boss has Glacial Shield which reflects all damage, DOTs, included. SO I usually switch to the 51 pally on that guy.)
anyway, this is long winded enough, but I may come back and create a post with my build.