Amarillo is a city in Texas.
West towards Albuquerque
There really is no best good ramp in Amarillo catching traffic to Albuquerque. Western Street entrance seems to have the most services catering to long distance traffic (fast food and gas stations.) This is an instance where an Albuquerque sign would be highly beneficial. Your best option may be going to the Pilot travel center on the far east side of town, although going here you will miss traffic coming from I27.
East towards Oklahoma City
There is a Pilot travel center located just out of town on the east side. Even if you get kicked out of the Pilot itself, this ramp is an ideal spot.
South towards Lubbock
Stand on the ramp at the intersection of I40 and I27. Catching the westbound I40 to southbound I27 traffic is preferable.
North towards Kansas
Stand along the edge of the US287/87 right where US87 and US287 (equivalent to Fillmore Street and Buchanan Street, respectively) merge. The speed limit is still only 45 mph here and this will assure you snag all the northbound traffic (you will be just before the bridge that crosses 15th Avenue.