Crochet - Granny Spike Stitch - leaves fewer gaps, because the second double crochet is crochet through the top of the second double crochet of the row below. Possibly use a dc,tc, dc pattern in the clusters? From Do It Darling.
Need an afghan and quick? Check out the Marvelous Mile a Minute Afghan Pattern! It'll take you next to no time to crochet and will look fabulous when you're finished. It's an easy crochet blanket pattern when you're in a time crunch.