First off, the humble Rhino, nuff said...
On a serious note, unlike Space Marines, Sister of Battle rhinos are often used quite a bit, due to the fact that Sisters are a tad more fragile than Space Marines. Nothing is different though, still the same old Rhino, just with Sisters of Battle iconography.
The second option is the Immolator, whilst a little different is pretty much the same as a Space Marine Razorback, except it is only able to take Twin-Linked Heavy Flamers, Twin-Linked Multi-Meltas or Twin-Linked Heavy Bolters. However the Immolator has one little wargear buff to its Heavy Bolters, Inferno Bolts. No not those amazing AP3 things that Thousand Sons use, these Inferno Bolts simply allow re-rolls to wound, not a awesome as Thousands Sons, but still pretty good.
Now the one thing the they have going for them is that all Sisters of Battle tanks have Shield of Faith, thus they all have a 6+ Invuln. save which on a tank is quite handy. The other wargear upgrades they can take are ok, but nothing spectacular.
I personally don't use transports for my Sisters, I only ever use the Immolator and even then only to transport Dominion Squads. But thats just me, they are ok transports, but not great, but I mean Marines don't get any better, I know the new codex may change things but still, these have been serving Space Marines for years and they still win battles.