Amateur gear is easier to use and has many more features while commercial gear has better RF performance.
I'd simply say 'Better performance'. Battery life, TX duty cycle, audio quality and volume, environmental and damage withstand specs, sensitivity, button screen printing lifespan..
Here's a list in the order they occurred to me...Some have already been mentioned but here goes:
Tough. I want to be able to toss my radio into the passenger seat as I climb into the car. I want to know that a few minutes of drizzle won't ruin my fleet. I want to swing that radio round and round by the antenna for comedic effect without risk of a depot repair.
Upgradeable firmware gets better and better.
P25 for highend radios.
Superior audio, like not even close. I use an Astro Saber as my primary scanner for Chicago PD. Not too easy to set up initially (compared with a scanner) but now that it's done, awesome rx radio. Scanner and hammy radios are simply laughable in side-by-side comparison with commercial rigs.
Honest-to-goodness priority scanning.
Speaker mics that can withstand my rough treatment. The elevated antenna on public safety mics for UHF rocks, too.
Over on the HF side o' things, I have a couple pros, too.
Killer speech compression.
Wicked DSP.
Standalone ALE capabilities.
Wiki link
I don't mind saying I like the underground nature of programming and upgrading capabilities. Nuff said.
Finally, there's some social aspects I enjoy. The hobbyist Motorola crew is smart and generous and I've made a number of friends both online and IRL.