Overall i like plastic the best.
It's lighter, easier to assemble, doest give you bended parts like the old metal products
(example: the good 'ol chaos halberds are a disaster to get straight as you order them they are bended as what cos they are in a bag!)
Drop a plastic model and you got nothin' drop a metal model and your lucky to have it in a least 3-4 pieces, try a thirster or obli for fun