Warne definetly.
Australian spin bowling stocks are in shambles. Macgill is bowling pies, as is Dan Cullen. Cullen Bailey, Aaron Heal, and to a lesser extent Nathan Hauritz (in OD) are the only spinners who've bowled well this season imo. Cameron White hasn't bowled near enough to be considered, despite being touted just 2 seasons ago as the man to take over from Warne.
Whilst for a replacement for the mighty Pidge, Johnson, Bracken, Tait & Hilfenhaus are all champing at the bit and raring to go if, and when they're given an opportunity. ATM i'd personally have Tait as the last in line of those 4. Hilfenhaus has been a machine for Tassy, as has Bracks for NSW, whilst Johnson has bowled well in his limited time with QLD this year. Tait did play well against Eng in the tour games, but apart from that, he's only produced 1 other spell of note against NSW.
Both Warne & McGrath are legends though, and whoever is chosen to take their places come selection time will have gigantic boots to fill, and enourmous expectation placed upon them. Whoever it is, i hope for their's, and Australia's sake, they don't buckle under the pressure, and can make a mark in the international arena.