It depends on what you mean by quality. In my experience, almost every monitor Apple bothered to put their logo on was at the very least "pretty good" - most that now survive were excellent.. Even the "bad" ones are, really, fine monitors, just, budget-oriented. I'm guessing something like one of the Performa branded monitors is going to be about equivalent to that Philips monitor you have. (In fact, I believe one of them might have been a badget Philips display, I've seen other logos and HD15 VGA cables on some of the Performa and budget oriented Apple monitors.)
The AudioVision 14 is the same display as the M1212, just with the (excellent) speakers and the additional connections. If you're using onboard graphics on a 6100 variant, and you don't have a DOS card, the AudioVision 14 makes perfect sense to use. If you can get one, do it. They're great.
The Multiple Scan 14 and 15/15AV are other reasonable options for a setup like this. They're budget oriented shadow mask monitors, they all have speakers, but among them the 15AV are the most worth using, followed by the 14 and the MS15's speaker is probably better ignored for gaming purposes, in favor of headphones or dedicated speakers.
Other Apple monitors to look for that are "excellent" or "high end" would be the Macintosh Color Display 16, which aren't super common in my experience but are very nice, and the Multiple Scan 17 and 20, which are trinitron displays, as well as the Apple High Resolution 13-inch color display. There was also a 640x480 monochrome 12-inch display, which, if you can find it, is probably worth it. Any newer display from Apple will probably also be fine. Some of the 17-inch monitors after the Multiple Scan 17 were more budget oriented and switched to shadow-mask tech, but I found them to look good when I've seen them. (I've had some face time with a 1705, a 720, and a 1710, and the 1710 is arguably better than the 1705 and 720, but are still pretty great, all things considered.)
One thing to be aware of, now that I think of it, with the 16-inch Macintosh Color Display is that the 640x480 mode on it will end up displaying in the center of monitor, so if you're going to be predominantly at 640x480 for gaming purposes, the MCD16 might not be the display to get. The other thing with the 6100's onboard video is that it is limited to 832x624 as its max res. Though, if you have the A/V card or either of the 7100/8100 HPV graphics cards you can get 1152x870, which looks just gorgeous on a Multiple Scan 20, the monitor originally introduced to sit at the top of the display lineup alongside the 8100. (All of the Multiple Scan displays will scale the picture up and down per the resolution you choose on them, which might make any of them better for predominantly 640x480 work than any Macintosh Color Display, asides from the 14-inch one (the M1212).
There's the 12-inch color monitor for Mac but it's 512x384 and so you'd have to want to run a lot of Compact-era software on like an LC with system 6 or 7.1 or whatever for that to be specifically relevant, although they are fun and they do still work out until like the beige G3s.
Pretty much any of those new monitors will probably look a lot better than any low end monitor so I'd say it'd probably be fine.
The thing that makes the M1212 and other "good" or "high end" Apple monitors what they are is that they're based on trinitron technology, which is Sony's high end monitor technology. (later ones are based on a similar idea from another company)
The other thing I tend to recommend thinking about looking at is much newer LCDs. I have a Dell P1914S and I've found that it's pretty good in terms of scaling lower resolution output and weirder resolutions. (Though the last time I used it on a vintage system was with the Sun, outputting 1152x900, so I don't know off hand what it'd look like at 640x480, 800x600 or 832x624.)
The biggest problem with the, uh, biggest displays is that they're moderately difficultt o find and ship, and so you might think about substituting a search for, say, a Multiple Scan 20 or any AppleVision display for something like a Dell P780 or similar. Basically, normal high end PC displays. Dell UltraScan, Gateway CrystalVision, Compaq had a similar line, HP had a similar line, and so on. Most of these would be Trinitron based, and often they directly used Sony's enclosures as well.
