I've used both and decided to use Fortes4Lazarus.
1. I wanted a report with two columns. This was not easily done in LazReport. In Fortes I used a two column grid as a work around. In both cases it was not possible to get "newspaper style" columns.
2. Fortes seemed to give me better control over the placement of the report elements, but this may just to me.
3. Fortes has a bug / memory leak in its use of bitmaps. This is fixed in the attached files.
4. Fortesd' documentation is sparse and in Porltuguese which makes the learning curve rather steep.
To see an example of what can be done check out the (free, but commercial) evaluation edition of SiP (a Simple Inventory Program)
You can download it from
www.fitall.com using the menu selections "Downloads > SiP" and then click on the appropriate link.
(Note: the evaluation edition does not allow saving or printing of the reports, which are generated as pdf files.)
Edit: added attachment.
Edit 2: In the attached files search for JR to find my changes.