I fly both Pattern and imac, and I love doing both. however I am still in college and I cant afford the best equipment in either class- I have a 1/4 scale cap, priced about $1200 rtf, and a widebody 60, priced about $900. I fly advanced Imac and pattern. I am much more competitive in pattern because the biggest plane can only be 10" bigger than mine, ignoring the cost. Imac is so expensive, that for a 33% plane would cost near $3000, to have the same competive edge that I have in pattern with a 800-900 dollar pattern plane.
If you are going to go all out, they are both very expensive sports, over 5000 dollars- but for lesser equipment, pattern is a better alternative because of its size restriction. take it for what its worth.
that being said, I enjoy IMAC more, though I CD a pattern every year. (it was last weekend)