Not sure about the reviews for Media Player Classic-BE.
I see people complaining about things they didn't understand or switch on.
But for clarity I can explain the differences we need to worry about between the players (I have tried a few with youtube).
Note: as you are not watching via a web page, you don't get adverts or malware

For your comparison, my experience is based on using XP with a 32bit Athlon 2800 CPU + ATI Radion HD3600.
First, "Media Player Classic - BE" and "Media Player Classic - HC" are both newer versions of the old "Media Player Classic" project.
They have a few annoying differences and so I actually use them both.
I use the "BE" version to stream Youtube, and the "HC" version to stream Twitch.tv
Both can decode Youtube MP4 and webm streams, but "BE" recognises the normal links when pasted as a file location.
All branches of MPC are still small compared to the alternatives.
All versions allow you to change the video decoder settings and rendering options for more speed, or more functionality.
If you choose "Save as.." from the file menu you can save the file to a folder.
Unfortunately this saves from the net, not from the temp data, so It can double the amount you download.
Next is the main rival VLC.
VLC is very flexible and also recognises Youtube links pasted as a "Network Stream"
Just like Flash, VLC has hardware decoding but only for DirectX10/Vista up.
You can use it in XP, but MP4 HD streams will still stutter.

If your GFX card does not have any DX9 HW decoding functions, then the best way to watch HD video with no stutter is kinda simple

If your monitor can go big enough, change your desktop size to the same width as the video, and it will no longer have to scale each frame.
This will help with all video players, inc. flash plugins.
(This is also what I used to do before I started using MPC-BE).

You can use any youtube downloader extension, to copy the long address of the actual files, and test any player you already use.
While on that topic, if you are looking for a media downloader that works on a few sites, try putting links here
http://en.savefrom.net/
It will give you links you can download or copy from in any browser. This is handy if you want to download on someone else's PC without installing anything.
It is available as a browser extension
http://en.savefrom.net/user.php
Glad you are using Malware bytes as a second opinion, although bare in mind that if you got hit by ransom-ware that encrypted your drive, there is nothing it can do afterwards. You need something that stops things from getting in.
Having a backup is your only cure.
Time was, your browsing habits would keep you safe, but luck is becoming much more to do with it these days, as the hackers keep trying to use google and the other "trusted" hosts to reach out.
Keeping safe with XP will continue to become a minefield as companies finally stop support.
Unfortunately some of the ransom-ware now does not require you to actively click on it. Only that you see an advert or video that used some jscript to fetch the nasty stuff.
You can run browsers with jscript off, but most of the internet stops working properly

The are browser extensions that will let you enable it for just the sites you trust (none for IE).
As for the common belief that Microsoft Security Essentials is doing much good, I really think you should look at these pages and see how it compares to real AV software.
Recent tests
https://www.av-test.org/en/antivirus/home-windows/
Last specific XP tests
https://www.av-test.org/en/antivirus/ho ... indows-xp/
Microsoft say that MSE is the "Baseline" to measure other AV to, as this is what you get with a standard Win7
The baseline is marked on this chart as the dotted line
http://chart.av-comparatives.org/chart1.php
Does that look good to you ?
This month the best free AV are Bitdefender and Avira (in that order).
Avira, and Avira free have been king of the hill more than anyone over the past year, so there is not much to split between them.
I believe both will run in XP.
I would pick whichever of the 2 does not make the PC too slow.

Worth keeping as another standalone second-opinion tool, is "Herd Protect". This is very small and handy because it uses multiple AV engines via remote connection (just like the Virus Total site).
It includes the Malware Bytes, Avira, Bitdefender, Avast, AVG....etc.
http://www.herdprotect.com
Final useful tip: Even though I theoretically know my sh*t, I still use a tool that scans all my installed programs for known problems, and if possible offers an update, or will do the update itself.
https://secunia.com/vulnerability_scann ... l/download
It should still install in XP, but if not I can find an earlier one that does.
OK. I hope everybody got something out of that, as this is useful to all versions of Windows.