I flew out with them last season and did have a holiday booked with them this year but had to cancel due to my dates having to be changed, however the flight that I did have booked was with Monarch through My Travel. If the flight number begins with MON then I think you can presume it will be a Monarch aircraft.
We were in premium last year and although we liked it, we paid an awful lot for the upgrade from Cardiff, over £200 each I believe (this year from Manchester its only costing £129). We did go back and have a look at the standard seating and there were no seatback TV's just the ones every so many seats up in the ceiling so to speak. There were no stops on route to Florida, it was a direct flight and we were told when we booked this years that it would be the same. There appered to be better seat layout at the back where the plane narrows and there were about 10-12 rows of a 2 - 2 seating plan, so if you go in standard depending how many of you there are, this may be a better option.
I do like premium on the My Travel aircrafts but was'nt absolutly sure it was worth over £200 per person on the Monarch aircrafts, although Im not sure what they are charging this year for the upgrades from Cardiff.