Current Status of most emulated platforms on the DS?

My apologies if there has been a topic like this recently, but I am unsure of if there is a real comprehensive resource to look up this sort of thing-- I've found a million tiny DS sites and nothing large and up-to-date.. anyway.

I am curious about the current emulation quality of a few systems with currently existing software for the DS. Most notably these:
- NES
- Sega Master System / Game Gear
- Game Boy
- MegaDrive/Genesis
- SNES
- Atari Lynx
- PCEngine

It's rather confusing due to having seen YouTube videos showing high-speed SNES emulation of some quite-stressful games like Tetris Blast and the less-stressful Super Mario World, with high-quality audio and graphical accuracy, then other videos of SMW running like garbage with layer priority issues everywhere, unplayably slow and with destroyed sound.

Looking into MD, I've seen videos on YouTube of Golden Axe and Sonic 2 running what looks like nearly full speed, with sound. Then threads here say there is no sound, and there is but it sucks, all in one thread.. A SNES thread says there are 3 SNES emulators then another says there are NONE. (What?!) It's rather baffling.

As a final question ... has there been any notable status on a homebrew web browser or port of an existing one? Or should I just go buy a copy of Opera?

Thank you for any assistance.