Are Dell monitors better than NEC or Samsung?
That really depends on the model. Dell's Ultrasharp line typically (but not ALWAYS, so check the specs first) uses higher-quality PVA and IPS panels, which are more color-accurate than the TN panels found in cheaper displays. Panel quality may be important to you if you intend on doing basic color correction work in your projects. Long story short, Dell doesn't make panels (and neither does Apple for that matter). They only build around them.
NEC has historically made excellent displays. The MultiSync 90 series is quite good, but it's a pro line and is priced accordingly. But the 2490 ($1,099) is handily one of the best 24" IPS-based displays money can buy.
Samsung is a mixed bag. They have a ton of cheaper TN-based panels that are typically stocked at local stores, but they also make more robust PVA-based models suited to higher-end users, for a price.
But anyway, IMHO, the two best quality 24" displays on a budget that you can currently buy are the Dell 2408WFP (PVA panel) and the HP LP2475w (IPS panel). They're both great-looking displays and have lots of features. Both can be had for under $600.