Yes, hepa's better. The air's gotta move to be filtered, and those
electrostatic ones don't move much air at all, plus every brand of
electrostatic I've tested sounds like a TV tuned to a dead channel. They
may be VERY quiet in the store, but once they start sucking in cat hair
into the wires, it's another story. YMMV with the noise, but you can find
a display model and test with your hand the comparative amount of air
moved by the electrostatics and regular fan-driven air filters.

Really, any fan-based hepa filter will do, just pick one based on the
size of the room it's rated for. However, to get a *quiet* one, you're
going to have to fork over some cash.

I recommend finding a store with display models to test or asking to open
one up and listen to how loud it is before you purchase. Most *are*
louder than regular fans.

Of course, the expense of replacement hepa filters is something to
consider also -- but my last one lasted 2.5 years before the replacement
indicator lit up.

Also, if the smell of the litterbox is really bad, you may need to clean
more often or find another brand of litter -- they're NOT all the same
quality in that regard.

HTH,

Honeywell has a combination of the two.  Good quality food has less odor
than cheap..  There are good quality litters that don't have heavy odor.
If your cat is fed right and groomed regularly, it should not smell badly/
Best wishes.   MLB