Building an Entry Level MTB. How should I choose suspension forks? I am new to Mountain Biking. I just bought a CRONUS HOLTS 330 (Hardtail) with Shimano gear system and disk brakes. Its a 19" frame with 26" tyres. All aluminium pretty light weight. The brakes are ok for now the only problem is the suspension forks. The forks are made by zoom and they suck. They dont spring back if they go in I have to jerk the handlebar upwards to bring them back to midway preload position. I am interested in buying a used rockshock air suspension fork but I cant figure out which ones are best for me because there are a million different types out there. Please help.
Also, the sram product matrix can be handy (y is cost, x is severity of impacts):



source: https://www.sram.com/sites/all/themes/sram_2011/st_rockshox/_images/products/product-matrix.png