Mac Family Tree 5.3 or Reunion

I have both. Reunion is the one to get. I find the route to the data entry in MFT far from obvious at several levels and as you necessarily keep hopping back and forward between panes this is a material problem.
The other problem is that at least two facilities in MFT, the Virtual Family Tree (a 3D all data picture) and the Kinship Reports ( who are your parents , grandparents etc, a printed list) are simply erroneous.
If you have a family with repeated marriages and children from each union, you will find VFT links the children of (say) 'her' children with his other wife, and KR makes the 'other wife the grandmother of her predecessor's natural children.
Both these features of MFT are not the core facilities. Those are the family reports and the individuals FT and/or descendants charts. However you could cause an upset if you sent such things out.
Virtual Family Tree in MFT is useful for envisaging the blocks of the family, say the people in "Baltimore" who are behind great gran Jenny and that small group in Tristan da Cunha who produced your father. The other point is that your FH data is probably amongst the most hard won on the computer so , aside from backups, it is prudent to have it in more than one database type. You should also make up GEDCOM file backups from time to time aside from native format bkps per Time Machine and whatever. If it keeps going MFT will resolve its problem so if you can persevere with Leopard you can persevere with MFT but don't rely on it.

My correction to my post. VFT wrongly links the children of 'Her' to the other other wife.

I was about to pull the trigger on Reunion and then came across MFT. It really looked nice and I did just a little testing with it and liked what I saw, and as Tony pointed out it's way less expensive. But it's good to know about the other issues with MFT.

No I haven't tried "mobile me". I don't use it at all. If you intend to publish, be careful about 'confidential' information and bear in mind that your family tree is other peoples as well and they may not like the publication. Don't put causes of death in it or someone will harvest it for biotech data.

I am not sure about Reunion but I believe MFT has it's own website for uploads. You could try that first. You could always pass the data to the LDS. They have rules against proxy baptisms of living persons and do help us all with FH.

You should also look at the French programme, Heredis. There is by the way a version in English and the very minor Gallicisms are nice in fact. It does have a members website. It is a solid programme. Whatever you buy do ask on it's forums about Mobile Me and also write to one of the main genealogy magazines. Your data is still safe in the programme so have a go with "Me".