I would recommend MacBench 3.0 (when it works) because you can then run it on an SE/30 too. If you go with MacBench 4.0, you can't use it on the SE/30. Maybe that doesn't matter to you, but that's my personal rule of thumb. Admittedly, I don't use OS 8 on my vintage 68K Macs, opting for speedier System software like 7.5.5 and below, which is perhaps why I've never had an issue getting MacBench 3 to work. I also prefer MacBench to other benchmarking utilities because it is the most extensive, taking almost 2 hours to complete. No other benchmarking app takes that long or does as many tests.
I do like Speedometer, but keep in mind version 3 and version 4 yield different results. So if you start with 4, be sure not to fall back to an older version 3.x because the results will be way off.
Also be sure to use Norton System Info too, as a part of Norton Utilities 3.5.x.
It's best to set colors to 256 (on color or grayscale Macs), and the cache to 128K, before testing.
There are other benchmark utilities too, like SCSI Director Pro 4.0, but that is mainly useful if you wish to focus on hard drive (or SCSI2SD) performance.