Okay, I'm using Wikipedia for scientific analysis here.
According to
Wiki, a large male Red Kangaroo "can be 2 metres (6 ft 7 in) tall and weigh 90 kg (200 lb)". This is the only dimensions that Wiki gives at a quick glance.
Wiki says the following in regards to the size of squids: "The majority of squid are no more than 60 centimeters (24 in) long, although the giant squid may reach 13 meters (43 ft) in length."
I went with everyone's favorite, the Spider Monkey, and
Wiki says the following: "Adults reach an average body length of 50 cm (20 inches) and a weight of 6.4 kilograms (14 pounds)."
So, it's a 20cm Spider Monkey vs. a 24cm Squid vs. a 2m Red Kangaroo.
It's so flippin' obvious that the Spider Monkey would win.