I've been playing a Drow ranger and chose beastmaster at level 3. After summoning each of the beast companions available, the giant spider is by far the most powerful by a significant margin. It has the most health, the most damage potential, a solid AC, a chance to poison, the second-best mobility behind the raven, and the most utility being able to enweb an area of enemies. Maybe the other pets catch up in power as you gain levels but at least the start there is no contest. It would make sense for the bear to have the most health, the spider to have the best utility with enweb and poison, the wolf to have the most damage, the raven to be the most mobile and have the highest AC (due to low hp, small size, high dex etc) and able to blind and the boar to have the 2nd best AC (behind the raven) with its thick bristles of hair and tough hide to allow it to charge in, run out and charge in again while hopefully causing attacks of opportunity to miss with its good AC.