Downloaded it myself and it said a years registration but I only got to January next year. never mind it was free.
As far as I know MalwareBytes pro is a one off payment so may be your best bet.
I use Emisoft Anti Malware but you have to pay every year for that.
Mine runs out next month thats why I downloaded Mamutu while it was free.
Whatever one you are thinking of getting check for coupon codes for them and you can always pick them up cheaper.