They are typically bigger at Nazare, but it all depends on the swell. Its not impossible for Mavericks to receive a swell that could create waves bigger than whatever Nazare has received in the last 20 years, but it's less likely.

However Mavericks is definitely the "nicer" and gnarlier wave of the two imho, Nazare is massive but has no shape, so they just surf the shoulder for 5 seconds and kick out. Mavericks has much nicer lines.