For heavy duty use Snap On makes a good one, the Schumacher and Century don't hold up in commercial use.
Especially if you try to charge a dead battery in "HI" the amp flow will smoke the rectifiers, Century told me a dead battery should be charged in LOW for 20 minutes before attempting to boost start. I had 2 Century's that I threw out to scrap because I got tired of fixing them. They came with crappy cables, which I replaced with a good jumper cable cut in half.
I have a small Schumacher trickle charger just die last week that I used to keep the generator battery charger.
I have another "smart charger" that is worthless because the smart charger types won't charge a dead battery unless they sense an existing voltage.
Tony