The range and the spread of Zermatt is difficult to beat in my view. I think you might find Verbier a bit claustrophobic if you are used to that. Verbier has some challenging stuff, interesting if you want to push your level, but not recommended for the blue slope types.
Both resorts have excellent slopes and on-mountain restaurants etc. Of the two I’d say that Zermatt has much better connections between its various areas. Verbier can be challenging some times.
Also Verbier has many more hoo-ray Henrys, Zermatt is much more international.
Never skied in Zermatt yet (the shame....) but if you are looking at Verbier, mind that the 4Valees ski area actually spreads across to Nendaz, Veysonnaz and Thoyon - and then there's also Tzoumaz and Brunson areas on top. There is plenty to ski about. If you are looking for size of the ski area, "portes de soleil" is also very, very big (when there is good snow in the low areas)
Only bemols (for me) would be that A) the link downhill from Chassoure to Tortin/Siviez is a yellow non-groomed slope that is too difficult for my skill level so I prefer to go down on the gondola (which is but a small inconvenience) and B) the slopes going down into Verbier itself get very crowded and are not very pleasant.
You would probably like Verbier if you are into hardcore off-piste skiing as there are dedicated areas one can adventure about