Looks like Vodafone have a discount on their 100/20Mbps NBN plan - $20 off for the first 6 months. I'm with ABB atm but I'll swap to Voda for the discounted 6 months then back to ABB to take advantage of "new customer" deals.
No contract, and has an optional free modem, though there is unfortunately a modem fee if you leave Vodafone within 36 months ($5 x remaining months). One pro of their modem is the 4G backup (Max speeds are 12Mbps for downloads and 1Mbps for uploads).
Offer ends 21/4/20. Don't forget cashback (CR $35, SB $30).