I did face severe technical issues during my last GMAT (Online) attempt, which might have lowered my score by 10-20 points. I have seen a couple of posts on the forum from other people who have faced similar issues.
I am still waiting for GMAC to respond to my email. They seem to be making the most of their monopolistic hold of the market.

If we were to contrast taking the GMAT at home with taking it at a test center, both options have their advantages and disadvantages.
Anxiety: I feel that taking the test at home tends to reduce anxiety, but doesn't eliminate it completely.
Noise: This is something you can't control. In my case, some construction work started next door just as I was starting the verbal section; this was extremely distracting and might have cost me 1-2 points. All things considered, at home you have greater flexibility to choose a slot that is silent (early morning / late evening).
Convenience: Considering the current pandemic situation, taking the test at home is way more convenient than taking it at a test center.
Whiteboard and markers: Take a look at the master thread on the forum. You should be able to find links to everything on Amazon. Also, during my exam, the proctor was more concerned with whether I was erasing the whiteboard properly than the make of the whiteboard and marker.
Conclusion: the GMAT (Online) is still my preferred option in the current pandemic situation.
My recommendation would be to assume that you will score 10-20 points lower than your average mock score and prepare accordingly.
Also, if you are using a slow computer, try to get the hardware upgraded. Upgrade your Internet connection, if required. Beg, borrow, steal.
TL;DR: GMAT (Online) is preferred. Assume a score drop of 10-20 points from your mocks. Upgrade your computer and Internet connection.