Thanks Cab,
Sorry I have no idea what the best bit is for MDF, I am a novice at this. I haven't cut much of it - but when I did used 2 fluted carbide end-mills. I think mine must be dull already as they seem to lift the very top surface skin of the MDF rather than cut it - or maybe a down-cutting bit would be tidier. The problem with my machine is that because it is home-made from MDF it is pretty flexible. Although it can move reasonably fast, itts flexibility limits the feed rate I can use in practice. So the feed rate is usually too slow for the spindle rotation speed - and the extra friction risks burning the MDF / dulling the bits.

Maybe speeding up the feedrate or slowing down your spindle speed on your router would extend the tool life? Some of the router cutter manufacturers have optimal speed/feed-rate charts for the bits they sell.