1. WebinarJam, when you want a published price and an offer on screen
The offer control is Active Offers. Room sizes and the trial terms are on the WebinarJam pricing page.
I'd start with WebinarJam when the price and the offer have to be on the same plan. Evergreen replays need the separate EverWebinar product unless that plan already includes them. The WebinarJam review covers the plans. The WebinarJam alternatives page places BigMarker next to the other rooms.