I have been using a DM3068 for a couple of years, and then got a 34461A... I liked it so much more that I bought a second 34461A. I do use the 3068 still, but I like using the 34461A enough that the boot time is worth the wait. If I'm in a hurry, I fire up the 34410A, which is very quick.
I really haven't noticed much fan noise from my 34461A's, but I can definitely tell when the 3068 is running.
As for the question about measurement differences, I'll have to check, but the Rigol might be able to test larger capacitors.
Although the Rigol has more dedicated feature buttons, I find the Agilent easier to use. It's certainly much easier when trying to access histograms and statistics (min, max, average, stdev...).
On the Agilent, I find the BenchVue software to be handy
Some users may find the Rigol fits their specific needs, but if you don't know and the price difference isn't an issue, then I'd go for the 34461A