Yes, face to face is best. It sounds like they aren't oppressive, so this should be possible to do the right way. As someone who has both quit jobs and had staff quit on me with varying degrees of decorum, the way you handle it determines the long term result. You may be surprised at their response. If they have any experience, they will understand it is in their best interest to end things gracefully. It may not be comfortable the first few weeks, but time heals all wounds, and you may be able to use them as a reference or connection later on down the road.

PS if they throw more $ at you, don't bite. Chances are you will quit again within 6 months. Good luck!