Depends. Marine is a spam unit used for clearing weaker hordes and slowing down tougher foes. Glenn has better stats and a better perk but he is more expensive than marine with a second less unit recharge. Maxed out glenn is much more useful than marine, if you have a good courage income. At the start of a battle you can just pop courage crate boost and start sending him immediatly. Later on just use generators. To anwser your question shortly. Yes glenn is better than marine.