Well, the EZ flex comes in MERV 10 and MERV 13. The "Cake Box" Cartridge style comes in MERV 8 and MERV 11.
In my opinion, I would suggest the MERV 11 Cartridge filter for two reasons.
1. With the EZ Flex filters, there seems to be a potential issue of the filter loading up and air bypassing due to the filter being collapsible.
2. The MERV 11 is medium range. On select systems, the MERV 13 can be too restrictive and cause severe airflow problems.
This is simply my opinion. The correct way would be to call your contractor and discuss. He can take several static pressure readings on your ductwork. He can then take the readings from your duct work and compare them to the manufacturer specs on each filter. With that info, he can decide what filter will provide the best filtration with the least resistance.