They are basically the same. The Horizon entered service in 1990, the Zenith in 1992.
They are both 46000 ton ships, have the same layout, etc.
I have sailed both but was on the Horizon for the 2nd time a few months ago and it had been well maintained. From reading posts re / the Zenith, it too has been well cared for.
You wouldn't go wrong on either, keeping in mind they are not new, glitzy mega ships with all the bells and whistles some ships have today.
If all else fails, flip a coin.
Which is less money for the room you want? Haven't been on the Horizon but the Zenith was fun. Just know that she is 11 years old and has a different style than those ships built in the mid-90s and turn of the millennium.
Have done the Horizon twice, never on the Zenith. Last time on the Horizon was last month. Enjoyed it a lot. Chose the H over the Z because of the time it spent in the ports. Check the itinerary closely. We thought we'd rather be in Hamilton longer than St George. Our preference. Also for the first time we participated in "Harbour Nights" on Front Street in Hamilton. This is on Wednesday nights only. Crafts, singers, dancers, performers, food, shops open late, etc. Lots of fun for everyone.
PS - The Horizon was well maintained and managed. I'd choose it again for Bermuda.
Been on Both Horizon and Zenith and loved it. the ships are smaller to the others of Celebrities but they are well cared for...
Commodore Caribe 1992
RCCL Nordic Empress 1994
Big Red Boat Oceanic 1993 94 95 96
RCCL Grandeur of the seas 1997 98
Windjammer Polynesia 1999
RCCL Enchantment of the seas 1998,00,03
Carnival Sensation 1993
Celebrity Zenith 2002
Celebrity Horizon 2003 Note* Booked for the Horizon 11 night caribbean cruise
and planning another for March 2004