I would like them ranked by tier, and if they share a tier, by viability in that tier. Singles, normal rules. (Also, I already know that Regieleki is probably going to win.)
Regieleki (OU) Regieleki takes the top spot. It's the fastest Pokemon in the game (can outspeed many scarf users and max speed investment). Has a decent electric movepool but not much outside that but its ability Transistor further boosts the power of those moves
Registeel (RU) Far below Regieleki is Registeel, and on a personal level, I think he is great. Good defensive typing and bulk make body press sets lethal, it also has stealth rock to set up and can mess with defog users such as togekiss and crobat. However it is reliant on leftovers for recovery so knock off can set it back, also meagre attacking stats make it reliant on toxic to do any damage thus making other steel types like metagross and steelix stiff competition.
Regidrago (NUBL) Although Regidrago has a mammoth 200 HP, its average defensive bulk negates that, however, regidrago makes a good late-game dragon dance sweeper but it's reliant on its counters being removed and thus has to rely on heavy teambuilding around it. After dragon dancing, it can 2HKO togekiss with thunder fang. However, its average attack stats even after dragon dancing leave it to unbale to leave dents in the likes of steelix, galarian weezing, and diance.
Regirock (PU) I use regirock in SWSH and can say for the most part that it's decent. Its incredible physical bulk and access to stealth rock make it a great physical wall. It can check a ton of threats in the tier such as archeops and and togedamaru with body press. However it struggles against common wallbreakers because of its poor defensive typing, secondly, it lacks recovery making it reliant on leftovers like registeel. Lastly, it faces stiff competition from Gigalith because it gains a special defence boost under its sandstream when it enters the battle.
Regice (Untiered) This one pretty much speaks for itself; ice types are normally never good and regice is no exception, it is reliant on heavy-duty boots due to its stealth rock weakness, however, its movepool is a bit wider than some of the other Regis
Regigas (Untiered) Probably the most obvious one, slow start cripples this thing so much to the point that it's unusable, and heavy support to try and stall out the slow start. However, with all the horrible things said it's a decent spikes utility mon.
1.Regieleki has a solid niche in OU thanks it's blistering speed, access to rapid spin and high power. 2. It can very easily take over games once the ground type has been taken down or chipped enough. 3. It has a niche on Hazard Stack teams alongside Galarian Zapdos. Spikes and Stealth Rock helps it wear down ground types, and it baits in Landorus-Therian for GZap to get an attack Boost with Defensive. GZap can also deter some defog users thanks to its ability defiant. Spin lets you remove opposing hazards while keeping your own, unlike Defog. Regieleki Hazard Stack: https://www.smogon.com/forums/threads/regieleki-sun-peaked-1-2144-ft-venusaur-torkoal.3704196/ 4. It has also been used on some Semi Rain teams during OLT as it outspeed Scarf Kart, provided speed control and could bait in ground types for rain sweepers to get easy entry. Semi Rain w/Regieleki: https://www.smogon.com/forums/threads/regieleki-semi-rain-peaked-1-2131-ft-specs-pelipper-barraskewda-updated-post-kyu.3687991/ Standard Moveset Regieleki @ Heavy-Duty Boots Ability: Transistor EVs: 16 HP / 64 Def / 252 SpA / 176 Spe Timid Nature - Thunderbolt /Electro Ball - Volt Switch - Rapid Spin - Ancient Power 176 speed evs outspeed Base 110s at +1(usually scarfers). The bulk investment let's you survive LO Bisharp Sucker Punch. The rest is dumped into Sp.Atk. Ancient Power chips Landorus-Therian. Regieleki is the only to be ranked on the OU and Ubers VRs at present, making it the best Regi in competitive singles. Source: Experience. Regieleki has up to date smogon analysis yet.
