Comparison sites list dozens of mobile brands, which makes the market look far more varied than it is. Newcomers choosing a SIM in their first week rarely know which underlying network a given brand rents from, and that is what determines coverage at a specific address.
There are only three real mobile networks in the Netherlands — KPN, Odido (the T-Mobile/Tele2 merger), and Vodafone — and every other provider you'll see advertised is a virtual operator renting capacity on one of those three, usually at a lower price but with lower service priority during congestion. KPN's network carries Simyo, Youfone, Budget Mobiel, Lebara, and several supermarket-branded SIMs; Odido's carries Simpel and Ben; Vodafone's carries Hollandsnieuwe and a few smaller budget brands. There's no single best value pick because it depends on what you're optimizing for: coverage in your specific area (rural regions can differ meaningfully between the three networks), whether you need 5G, how much EU roaming data is bundled in, contract length versus rolling monthly, and customer service quality, which tends to be noticeably better on the parent brands than their budget offshoots. A sensible way to shop is to check which underlying network a candidate MVNO actually uses, confirm coverage at your address on that network's map, then compare price per GB across a few names on that same network rather than treating "cheapest headline price" as the whole decision.