When I can only bring one deck with me, its typically Rin and Seri because its fun, personal, and not an overly powerful deck in my gauntlet
Even if Fastbond just puts two extra lands into play turn 1, you have a two-turn advantage over your opponent
Here are the general rules of thumb I follow when addressing this question myself: If my deck has green, the best mono green mana ramp spells are usually better than my multicolor options
The Ward ability keeps him well-protected from cards that hurt or eliminate chosen characters, forcing opponents to fight him head-on
I have to say, Studio X at Wizards of the Coast (WotC) has been hitting some serious home runs when it comes to Gruul commanders, to the point that I now have slightly more Gruul than Golgari Commander decks in my collection, despite being a huge Golgari fan for decades