Sorry it took me so long to respond.
We had previously used excel and the budgeting managers loved the experience from a UI (user interface) and UX (User eXperience) standpoint - i.e. they were familiar with the interface and the overall experience of it since it is a familiar UI leeds to better satisfaction, fewer input errors, less training requirement, etc.. The downside is that to fully implement a robust excel solution, you have to have someone at the switch tweaking and rolling up the information which is timely.
Forecaster, while probably ok for very large beaurocratic organizations, does not lend itself to changes during the budgeting process. combine this with the massive bugs that we experienced that inflated our reported budget in 2008 vs the REAL budget (it was off by more than 5% due to calculating benefits for people that didn't exist).
I only know about Solver what i've read and my implementation team has shared with me - it is excel based, but has a direct feed linked into your ledger system (works with SAP, Dynamics, and a slew of others if you belive the marketing) which is another hole from the Forecaster standpoint. Forecaster probably works great if you have the backend infrastructure to support it, but it wasn't worth the investment we made into it and our "microsoft shop" office hated the UI as well as the result.
HTH