Rogue: It’s hard to utilize sneak attack in spiked armor and with short dwarven legs. Rogue fighting styles are the opposite of what you are about.
For a Grapple Barbarian like a Battlerager, I would certainly rate a 1 level Rogue dip as higher than Purple.
The big thing you gain is
Expertise in Athletics. This doubles your proficiency bonus to your Athletics checks, which when combined with Rage's Advantage, makes your grapples/shoves almost certain to succeed, and nigh-impossible to escape from.
Sneak Attack is very useful too. It's not hard for a Battlerager (or any Grapple Barbarian) to utilize Sneak Attack. Sneak Attack does require you to use a Finesse-capable weapon, so that limits your melee weapon options to something like a Dagger, Rapier, Scimitar, Short Sword or Whip. But that's not a problem, since Grappling requires a free hand, and therefore you can only use a 1H weapon to attack someone you've Grappled anyway. And while the idea of a Battlerager using a dainty Rapier may seem odd, mechanically the 1d8+STR from a Rapier is the same as the 1d8+STR from a Warhammer or Battleaxe or Longsword. You could always refluff it as something like a Basket-hilted Broadsword, for a Highlander Battlerager. Or for a Steampunk Battlerager, that Rapier is refluffed as a spring-loaded retractable metal spike that deploys out of the forearm of his spiked gauntlet. Or with a Scimitar or Short Sword refluffed as a Cutlass, you've got a Pirate Battlerager.
As long as you're using one of those qualifying weapons, Sneak Attack applies when you have Advantage on an attack. Keep in mind that
Reckless Attack grants you Advantage. So therefore, that's extra damage every round that you're Recklessly Attacking. You also gain Advantage on a Prone enemy, and a Prone Grappled enemy can't stand up. So if you Grapple an enemy and then Shove them Prone (or vice-versa), that's Advantage on every attack until the Grapple ends, which means Sneak Attack will apply every round you're attacking a Prone Grappled enemy, even without using Reckless Attack. (There are other sources of Advantage too, from certain spells and other enemy conditions.) Sneak Attack also applies when you don't have Advantage but another ally is within 5 feet of the same enemy, which means if your party contains at least 1 other melee fighter, or your party has a Summoner caster, you and one ally or summoned creature can both gang up on one enemy to trigger Sneak Attack even without Advantage.
So the 1d6 extra Sneak Attack damage from 1 level of Rogue could potentially apply to a large number of your attacks as a Battlerager, provided you're using the right weapon. And it means that Scimitar or Short Sword is now doing the same damage as a Greatsword (2d6+STR). Or a Rapier is now doing
more damage than a Greatsword (1d8+1d6+STR). And unlike a 2H Greatsword, those 1H weapons can be used against an enemy that you're holding in a Grapple. Even if you don't plan to utilize Grappling very often, and want to play it more defensive, it still allows you to have Greatsword-style damage while wielding a Shield for +2 AC.
1 level of Rogue also gets you a few other skill-related benefits, like an extra skill proficiency, plus Thieves Tools proficiency, plus Expertise in a second skill besides Athletics. (I'd probably choose Perception.)
All that at the cost of merely delaying your Battlerager progress by 1 level.
Therefore, I'd rate 1 level in Rogue as Turquoise. Better than a Fighter dip, IMO. Not quite mandatory Gold, but a seriously good choice that will noticeably increase your grappling capability, add damage to most of your attacks, plus net you some other handy skill benefits to boot, all at a small cost of a slight delay.
Higher levels of Rogue aren't usually worth it, though. 2 levels of Rogue only gets you Cunning Action, which isn't of any use to you. Bonus Action Dash could be situationally useful, but you get that anyway at Battlerager 10. As a frontliner you will hardly ever be Disengaging. And you have Disadvantage on Stealth from your Spiked Armor so you won't be Hiding. Besides, you have other uses for your Bonus Actions, like making Spiked Armor attacks.
3 levels of Rogue does open up a couple interesting options, though. First, you get an extra 1d6 to your Sneak Attacks (+2d6 total), so your Scimitar/Short Sword is doing 3d6+STR damage on most attacks, and your Rapier is doing 1d8+2d6+STR on most attacks. You can also choose a Rogue Archetype. Mastermind, Inquisitive, Swashbuckler, and Arcane Trickster don't offer much of anything to you. Assassin could be somewhat useful, if you have a way of reliably generating surprise, allowing you to do a decent amount of extra damage in the first round of combat, provided you have a high Initiative. I'd recommend the Alert feat paired with a high DEX if you go this route. Thief could be slightly handy for exploration, with a bit better climbing and jumping ability to complement your high Athletics and STR score, and combined with the Healer feat and a Healer's Kit, you could make a decent backup healer with Bonus Action Use An Object.
Scout is where it gets really interesting. It gets you Proficiency and Expertise in a couple nature-related skills, and more importantly adds the interesting feature of Skirmisher. With this, you can move up to half your speed when an enemy ends their turn within 5 feet of you. If you have an enemy Grappled, they can't move, so they will have to end their turn within 5 feet of you. You can also drag a Grappled enemy with you when you move, although it cuts you down to half your speed. So if your DM is willing to play ball with the concept (which seems to work RAW), you could potentially Grapple an enemy on your turn and drag them half your speed. Then on their turn, when they end it still Grappled, you could drag them another quarter of your speed. (Half speed for Skirmisher, and half of that for dragging a Grappled enemy.) This could be really good when combined with a party caster running something like Create Bonfire, Cloud of Daggers, Spike Growth, or a similar spell, with you repeatedly dragging an enemy through a damaging spell area and triggering that damage, on both your turn as well as on the enemy's turn. This would work especially well with speed-boosting feats like Mobile or Squat Nimbleness.
So if you have the ability scores and feats to take advantage of Assassin or Thief, or you can work up a party strategy like the above for Scout, 3 levels of Rogue for an Archetype and extra Sneak Attack damage could potentially be worth the larger delay in Barbarian levels. Otherwise, it's not worth going past 1 level in Rogue.
