i dont usually have a spotter, if i fail on the last rep i just roll the bar down onto my legs and stand up with it. dont worry about getting crushed i've done this with 180kg and survived unscathed lol.
IMO free weights are always preferable to machines except for flyes as you lose resistence halfway through the movement with free weights.
read this and apply the principles for your chest workout...
http://www.musclechat.co.uk/viewtopic.php?t=2071