I hold individual Corporate bonds. I used to hold Bond mutual funds, but saw those never appreciating in value much, even when interest rates were falling substantially (2008-2015). Found out mutual funds do bit more trading and many don't even hold bonds til maturity. Some of the things I've observed:
1) Even though bonds are suppose to be safer (relatively) during a downturn, in a panic they act just like equity. March 2020 saw many/most of my bonds swoon just as much as Equities did. Bonds didn't stop bleeding until after uncle Powell interjected and said he would buy off all bonds (that need to be offloaded to big daddy, aka Fed).
2) AAA-rated bonds don't pay much interest. You get safety (again relative), but almost no return after inflation.
3) Same with municipal bonds. Most pay very little interest. Ones that have higher coupon from years ago, their current prices are way above par. Also they are not safer, imho. If not for the latest federal bail-out ($2T stimulus), many were at risk of serious default.
4) BB-rated bonds do pay decent effective yield. Or at least they did when I bought those 3 years back. But then they also carry higher default risk. I avoid all issuers that are in real-estate, finance (other than TBTF Banks) or student loan (Sallie Mae et al) industry.
5) Most of my individual bond holdings are industrial, that Uncle Sam will move earth and heaven to keep them float. Think Boeing, FedEx, International Paper, General Mills, ATT, TBTF Banks etc. Basically you want to look for issuer that are bit risky (for better yield) but know uncle Sam will come and save them if they were to get really stressed.
6) if you think interest rates are headed to 5%+ in next 5-10 years, then avoid bonds.
7) I personally think that after next Fed flirtation/attempt of normalizing rates a bit (2-3-4 years from now or whenever they try that), market will swoon and fed will just bring the rates back closer to 0. That's why I hold bonds. Another factor in my mind is Federal debt. In next 4-6 years, looks like Federal debt is headed towards $40T. Even if interest rates were to rise to 3%, that would be roughly $1Trillion+ in interest alone for uncle Sam, per year. So uncle Sam will not let interest rates rise for much longer if they even get there somehow. Because Math doesn't add up.
Just my observations... based on timelines of when I dipped my toes in bond world. Bonds do evoke different emotions for different people. For preferred, I just buy the index, like PFF.