Either should be fine. I think it is ideal for maximum ventilation to do a larger hood, but how that looks depends on the style you choose and whether the hood it is incorporated into your cabinetry. We used a 30" low profile hood with our 30" range, but we got a very strong one with a high CFM and it works beautifully.

I prefer a hood that matches up with the range size and it makes for a more uniform look when planning the surrounding cabinetry. Having said that, there is no hard and fast rule. I do agree with feeny, most people don't give enough consideration to the power of the hood when planning and therefore, most hoods are undersized for the job they need to do (undersized meaning low cfm's not physical size). Try to go with a minimum of 400 cfm.

If you are using a micro hood or 8/9" metal hood with cabinetry above, keep it 30. If it is a decorative hood, either metal 'chimney' style, or a matching wood one to your cabinetry, go 36".

M1503.4 Makeup air required.

Exhaust hood systems capable of exhausting in excess of 400 cubic feet per minute (0.19 m3/s) shall be provided with makeup air at a rate approximately equal to the exhaust air rate. Such makeup air systems shall be equipped with a means of closure and shall be automatically controlled to start and operate simultaneously with the exhaust system.

http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_15_sec003.htm

does anyone know what type of fan this miele uses?