I'd like to bring another Pokemon into discussion:
Milotic is a great Pokemon in this metagame due to its ability to check / counter a significant portion of the tier; it can even run an effective offensive set on spike-stacking teams!
What differentiates Milotic from Suicune is its access to reliable recovery, and what separates it from Slowking is its slightly higher SpD stat and significantly better speed, it also doesn't have those nasty weaknesses to Bug-, Ghost-, and Dark-type moves.
Here are the sets I've been using:
Milotic @ Leftovers
Calm Nature
248 HP / 8 Def / 252 SpD
Trait: Marvel Scale
-Scald
-Recover
-Haze
-Toxic
This set counters / checks a huge portion of specially based attackers, including Yanmega, Porygon-Z, Moltres, Mismagius, Houndoom, Nidoqueen, Reuniclus, Venomoth, etc. Basically, the key to this set is haze, which prevents bulky set up sweepers from walking all over it. Scald is also pretty neat to patch up Milotic's physical defense as is Marvel Scale should it come in to absorb a Scald from another bulky water.
Milotic @ Life Orb
Timid Nature
4 Def / 252 SpA / 252 Spe
Trait: Competitive
-Hydro Pump
-Ice Beam
-Hidden Power Grass
-Recover
I know this set looks strange, but it's really effective in practice. The entire premise is to pair Milotic with something that can set up Spikes (Froslass). Now, Competitive discourages the use of Defog considering that Milotic will gain a +2 Special Attack boost if it comes in on it. At +2, Milotic hits insanely hard and is really difficult to stop in the case of slower teams due to its fantastic coverage, bulk, good speed, and recovery. Just to give you an idea: +2 252 SpA Life Orb Milotic Hydro Pump vs. 4 HP / 0 SpD Virizion: 156-183 (48.1 - 56.4%) -- 34.8% chance to 2HKO after Leftovers recovery. So basically, not even a bulky resist with 91/129 defenses likes to switch in! Timid is essential due to that fact that Milotic sits in a trolly speed tier (81), which lets it just barely outspeed Jolly Gallade and fire off a powerful Hydro Pump.
I haven't tried out a RestTalk set, but I assume it isn't that bad with the sleep mechanics reverting. Once the tiers begin to settle a bit more and certain things move up (Raikou, Shaymin) and certain things get banned (Suicune, Kyurem), I expect Milotic to come out as a top-tier threat in this meta.