The current "gold star" release is 15.1.4M12a:
i have a 64M compact flash on 2811 router ,
I'm going to use c2800nm-advipservicesk9-mz.151-4.M12a.bin
thanks in advance
I don't know about anyone else, but I had a lot of memory leak issues with 15.1(4)M12a regarding DNS, eventually required rebooting every 24 hours... These are issues I did not have with 12.x IOS. you might consider grabbing the last version of 12.x you can get to have it on the flash also...