It's all about personal preference. MYT will be using a Boeing 767-31K. Interior wise, it's on par to what Monarch offer (either A300B4 / A332 or B763). If MYT were operating one of their A332's, it would be MYT hands down for me but they are on Hajj duties at the moment so there's not a lot in it really. For more information, have a look at the dedicated airline threads.
As Darren said the Kerala flight is a Boeing 767, these are not being repainted or having the seats changed as they are leaving the longhaul fleet in the spring\anyway. So will be MYT service till then.
Seats are personal preference. They are much of a muchness on MON's aircraft anyway. Personally, I'd go for any A/B or G/H as they are less closterphobic being in pairs.