ORAS are the most convenient games for EV training yet, primarily because the distribution of EV's in horde encounters is much more sensible than it was in XY. For each stat there's at least one route where 100% of encounters give only EV's for that stat, making it easy to pile up a ton of one kind of EV very quickly.

While there are plenty of guides on the internet that mention those routes, however, I was interested in routes that gave useful combinations of EV's instead--for example, when training physical attackers, I like to use Route 101 or Route 103, since they give me all the attack and speed EV's I want in one location. That in mind, I compiled a table of all the locations in ORAS, how many different kinds of EV's they give out, and what those EV's are. Click the name of a location to get a more detailed breakdown of the hordes that appear there.

This is the expanded horde data table, including information on which specific pokémon appear in hordes on each route, how often the different hordes appear, and so on:

ORAS Hordes by Route
Pokémon		Level	Encounter Chance	Base EV Yield
Petalburg Woods (HP, Speed)
	Wurmple	3	60%	5 HP
	Zigzagoon	3	35%	5 Speed
	Shroomish	3	5%	5 HP
Rusturf Tunnel (HP)
	Whismur	5	100%	5 HP
Granite Cave 1F (HP, Defense, Speed)
	Zubat	6	60%	5 Speed
	Makuhita (4)/Geodude (1)	6	35%	4 HP, 1 Defense
	Makuhita	6	5%	5 HP
Granite Cave B1F (Defense, Speed)
	Zubat	6	60%	5 Speed
	Aron	6	40%	5 Defense
Granite Cave B2F (Attack, Defense, Speed)
	Zubat	6	60%	5 Speed
	Aron	6	35%	5 Defense
	Mawile (OR)	6	5%	5 Attack, 5 Defense
	Sableye (AS)	6	5%	5 Attack, 5 Defense
New Mauville (Special Attack, Speed)
	Voltorb	12	65%	5 Speed
	Magnemite	12	35%	5 Special Attack
Fiery Path (HP, Defense, Special Attack)
	Numel	8	60%	5 Special Attack
	Koffing (OR)	8	35%	5 Defense
	Grimer (AS)	8	35%	5 HP
	Slugma	8	5%	5 Special Attack
Jagged Pass (Attack, Special Defense)
	Machop	10	65%	5 Attack
	Spoink	10	35%	5 Special Defense
Meteor Falls 1F 1R (Speed)
	Zubat	9	100%	5 Speed
Meteor Falls 1F 2R & B1F 1R (Speed)
	Zubat	20	100%	5 Speed
Meteor Falls B1F 2R (Attack, Speed)
	Zubat	20	95%	5 Speed
	Bagon	20	5%	5 Attack
Scorched Slab (Speed)
	Zubat	14	100%	5 Speed
Safari Zone, All Areas (Attack, Special Attack)
	Doduo	15	60%	5 Attack
	Oddish	15	35%	5 Special Attack
	Psyduck	15	5%	5 Special Attack
Mt. Pyre Interior (Attack)
	Shuppet	15	100%	5 Attack
Mt. Pyre Exterior & Summit (Attack, Speed)
	Shuppet	15	60%	5 Attack
	Meditite	15	35%	5 Speed
	Vulpix	15	5%	5 Speed
Shoal Cave, Low Tide (HP, Speed)
	Zubat	17	60%	5 Speed
	Spheal	17	40%	5 HP
Shoal Cave, High Tide (HP, Speed)
	Spheal	17	60%	5 HP
	Zubat	17	40%	5 Speed
Shoal Cave Ice Room (HP, Speed)
	Zubat	17	60%	5 Speed
	Spheal	17	35%	5 HP
	Snorunt	17	5%	5 HP
Seafloor Cavern (Speed)
	Zubat	18	100%	5 Speed
Cave of Origin (Speed)
	Zubat	18	100%	5 Speed
Sky Pillar (Attack, Special Defense, Speed)
	Golbat	23	60%	10 Speed
	Ariados	23	35%	10 Attack
	Swablu	23	5%	5 Special Defense
Victory Road (HP, Defense, Speed)
	Zubat	20	60%	5 Speed
	Aron	20	35%	5 Defense
	Loudred	20	5%	10 HP
Route 101 (Attack, Speed)
	Zigzagoon	2	95%	5 Speed
	Poochyena	2	5%	5 Attack
Route 102 (Defense, Special Attack, Special Defense, Speed)
	Zigzagoon	2	60%	5 Speed
	Lotad (AS)	2	35%	5 Special Defense
	Seedot (OR)	2	35%	5 Defense
	Ralts	2	5%	5 Special Attack
Route 103 (Attack, Speed)
	Zigzagoon	2	60%	5 Speed
	Poochyena	2	35%	5 Attack
	Wingull	2	5%	5 Speed
Route 104 North (Speed)
	Zigzagoon	2	95%	5 Speed
	Taillow	3	5%	5 Speed
Route 104 South (Speed)
	Zigzagoon	2	95%	5 Speed
	Wingull	2	5%	5 Speed
Route 110 (Special Attack, Speed)
	Magnemite	6	60%	5 Special Attack
	Plusle (AS)	6	35%	5 Speed
	Minun (OR)	6	35%	5 Speed
	Minun (4)/Plusle (1) (OR)	6	5%	5 Speed
	Plusle (4)/Minun (1) (AS)	6	5%	5 Speed
Route 111 (Defense)
	Sandshrew	11	100%	5 Defense
Route 112 (Attack, Special Attack)
	Numel	8	65%	5 Special Attack
	Machop	8	35%	5 Attack
Route 113 (Defense, Special Attack)
	Spinda	9	95%	5 Special Attack
	Skarmory	9	5%	10 Defense
Route 114 (Defense, Special Defense)
	Swablu	9	65%	5 Special Defense
	Seedot (OR)	9	35%	5 Defense
	Lotad (4)/Swablu (1) (AS)	9	35%	5 Special Defense
Route 115 (Special Defense)
	Swablu	10	100%	5 Special Defense
Route 116 (Defense, Speed)
	Zigzagoon	4	60%	5 Speed
	Nincada	4	35%	5 Defense
	Skitty	4	5%	5 Speed
Route 117 (HP, Special Attack, Speed)
	Oddish (4)/Zigzagoon (1)	7	60%	4 Special Attack, 1 Speed
	Roselia	7	35%	10 Special Attack
	Marill	7	5%	10 HP
Route 118 (Special Defense, Speed)
	Electrike	12	60%	5 Speed
	Wingull	12	35%	5 Speed
	Kecleon	12	5%	5 Special Defense
Route 119 (Special Attack)
	Oddish	12	100%	5 Special Attack
Route 120 (HP, Special Attack, Special Defense)
	Oddish	13	60%	5 Special Attack
	Marill	13	35%	10 HP
	Kecleon	13	5%	5 Special Defense
Route 121 & Route 123 (Attack, Special Defense, Speed)
	Shuppet	15	60%	5 Attack
	Wingull	15	35%	5 Speed
	Kecleon	15	5%	5 Special Defense