It depends on what you are doing. Loose ball bearings can be better rolling and smoother but aren't great for the weather. The few seals and things getting in the way of a bearings movement the better. Ideally for a track bike for say a Keirin event you would put minimal grease or some lube on it each race just so it is super smooth so you can edge out the competition since you don't have much else other than your strength and power. However for the practical everyday machine sealed cartridge bearings will be a better solution however I would save up to move a little further away from the absolute cheapest stuff.