Size
The Bichon Frise is much larger: about 6.8 kg (15 lb) as an adult, against 3.5 kg (7.7 lb) for the Maltese.
Shedding
Their coats shed differently: the Bichon Frise holds loose hair until it is brushed or clipped out, the Maltese sheds through the year.
Grooming
The Maltese needs more grooming, daily brushing, where the Bichon Frise needs brushing a few times a week.
Temperament
They differ most on loyalty (Bichon Frise: friendly with everyone; Maltese: sticks close to its people).
Alike
Both are rated the same on affection: a lap or leaning dog.