what makes a better first monitor?

In my opinion, none of the Monitors you listed I would consider for a first Monitor.

Mangrove Monitors, they are quite skittish and are very nervous Monitors. You're looking at a semi-aboreal/semi-aquatic Monitor. They spend a good amount of their time in water, so you are going to need a place where they can fully submerge their body in water. One they could swim in would be best. You're also looking at a custom cage too. One that can house a Monitor that can reach 3-4ft in length and sometimes as big as 5ft.

Yellow Monitors, you're looking at a Monitor that can get about 3.5-4ft in length, sometime even 5ft.

Some say these are pretty good monitors to tame, others say they can have a bit of a temper and be quite shy.

Dumerils are a larger monitor, easily reaching 5ft in length. They are known to be shy and skittish just like Mangroves. They are usually non-aggressive though. not much is really known about them. No one is sure if they are a common Monitor, or a rare one.

Monitors are hard to breed in captivity so most are wild caught. You can tame wild caught, but it takes a lot of effort. It's reported that it can take up to 3 years to tame a wild caught monitor.

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good lord, NONE OF THOSE are good choices. They're all three likely to be WC, parasite loaded and dehydrated. They're also all tropical arboreal, and get pretty big; think 3-5'.

If you're dead set on getting one of those, a dumeril's *might* make a marginally better choice I guess. You'll need, as an adult, a large arboreal enclosure with hides, moderate to high humidity and very warm basking spots, and tons of food. Good luck.

There are two major reasons to invest in a better monitor. First, it is most likely where you spend most of your time. Second, the monitor is the primary tool to view and edit your files.

The three major factors to consider in selecting a monitor are color gamut, bit depth, and calibration ability. Depending on the nature of your work, other factors to consider might include viewing angle, contrast range, and refresh rate (for video work).