On a cost for cost basis , ferry for us . Keeping an eye open for their every so often deals , get crossings with DFDS Dover- Dunkirk at around the £50 return mark . Example being , our next trip . Unless I"m doing something wrong while searching , then tunnel = £161 for best deal on our travel days . Ferry £49 return ( using a promotion deal ) same days . Far too much of a differential to ignore . Thats a fair few beers , meals or aires fees which can be bought with the difference in costs .
Comfort basis , have never used the tunnel when using MH , so really cant comment . Apart from saying , yes it would be nice to stay in the MH for the crossing . Also the bonus of the weather being irrelevant for crossing .However , its good to get in to one of the lounges on the ferry and relax for a couple of hours after our 2 hour drive to get to the terminal . Then reach France feeling rested and relaxed .
Convenience basis , it has to be the tunnel due to crossing frequency . Ferry wise , we have turned up early and been offered next crossing at no extra cost , so a bit of a bonus there .
The frequent traveller in the tunnel costs £430 for ten single tickets. You pay a £9.00 supplement for a MH making a return £104. An average normal booking made online is typically £120 - £140.
So ferries are cheaper. That said last time I went on a ferry Dover to Calais it cost c. £90.00 plus four breakfasts, drinks & items from the shop i.e. pretty much the same.