I sir have decided to subscribe to your publication! Where do I grind in the late 20s?
The rule is to keep mobs that you're killing 5 levels higher than your current level wherever possible.
An exception to the above rule:
1.) Mob clear speed and respawn rate outweigh shifting spots to maintain 5 level differential.
Examples being (MT WW cave, Most Bandit Camps, And the Golden Mercenary Camp and Cold Harbor grind areas)
Late 20's you should start in MT (level 33 area) The initial zone line has sets of 3 guards that are doable for a duo or a skilled solo. To the immediate east is a cave of fairly gnarly ass Werewolves, if you can manage killing these you'll get about 2% per pull.
Ultimately if you can't survive AOE packs of up to 10 mobs solo, you're generally beter off finding solo pull mobs like the imp camp in the AD lvl 40+ zone or the Giant snakes/Plants Werewolves, Ogrims, Ogres, Clanfears, Spider Daedra. Etc. If you can clear these higher HP mobs faster than a 3 pull you'll generally level faster as a result (like 10 minutes faster).
Also don't forget WW cave and Orc bandit camp both have quests which give you a companion that helps you fight, improving clear time without costing you the group xp penalty. I'd recommend not completing these quests until you grind your heart out with the companion in tow.