Capital gains are deferred. 

This isn't the stock market where the goal "is" to gain the highest return on an investment compared to other investments within the stock market. 

Given the current market, should I sell or continue to gain the benefits as it is paid in full?

You don't want to be paying taxes on your gains every couple years.

You can invest through the IRA account and your gains are tax deferred. 

@Peter MorganYou are eligible to take advantage of section 121 exclusion on the unit that you lived in.You are eligible for 1031 exchange / QOF for the unit that you did not live in.Whether you decide to do 1031 or not depends on the amount of gain and whether you will be able to find a replacement property in time.

I have one for an individual triplex, have an option on another empty lot, and own 3 contiguous properties with multiple lots that can be split or combined for up to a 75 unit/6 story building and in between so it's a tactic of mine to have projects in the queue and be able to hold/do something in a year or two once I clear past the capital gains timing. 

And if you move from land to constructed building you will gain depreciable basis.

I had to pay an engineer to do soil samples to see if the solid rock soil would support the weight of the addition.

I’m looking to own rental properties but I wanted to gain my cash.