In the early 1990's, we had the spreadsheet wars and Excel won that battle. The OLAP market is going through the same process but the most likely outcome will be the Microsoft Analysis Services (AS) platform. In the mean time, the following are some of the OLAP engine differences you could be considering for Analysis Services vs other OLAP products. There are many, but below are some.

Factor	Analysis Services	Other
Can you work with non-unique members in dimensions?        If not, do you have to create mapping tables and maintain these.        Does this increase development times and costs	Yes N/A N/A	No Yes Yes
How many dimensions can you have in a cube? OLAP Office Explorer™ has no limit as to the number of dimensions it can browse and is limited to that of Analysis Services.	128	<20
Can you add or delete dimensions in a cube easily?	Yes	No
When changing the cube structure, consider the impact on the reporting environments, i.e. do you have to update all queries/views with the relevant changes?	Yes/No	Yes
Can you handle large volumes of data?	Yes	No
Is there another non-Microsoft security model involved?	No	Yes
- Can you use Microsoft's Active Directory?	Yes	No
Can you combine current functions available in development tools in the equivalent of MDX? (Don't get caught in the non-industry standard dependency game)	Yes	No
Can you combine budgeting and forecasting into your solution?	Yes	Yes