Speed/agility is much more important, since they're the backbone of your return man. Raise them insanely high to take advantage of the early level majors. Don't start touching carrying until both are capped fairly high.
I like carrying as my 3rd most important attribute, especially if you're striving to be a "Spin" specialist (hint: you should be). It effects Spin brTk chances, normal brTk chances, and fumble avoidance. Basically, you're killing three birds with one stone. Don't be afraid to add equipment into it. Raise it to the mid 80's (w/ equipment).
I love carrying so much that I limit my strength to the 2/1 cap and compensate with increased carrying. After all, getting both too much strength and too much carrying is overkill and will detract from other areas in your build.
Just make sure your intense training agility as you work up speed, then intense train carrying as you work up agility, and you should do fine.
