I have tried JSB's and Air Arms field and mine prefers the Air Arms as for barrel cleaning mine does not seem to like being cleaned.
Just enjoy shooting it, despite all the negative comments going around about the FTP, it is a great gun to shoot.
ps I have had problems with my filler valve which I have now removed and fitted a Daystate type.
Zenith Air Arms FTP 900 Leup Comp
Feinwerkbau 800 X Leup Comp