Building a Dynamic Table in Marketing Cloud

You don't need to use either. HTML will not render a row if there is no content in its cells. I think this may only apply where the table has 0 cellpadding and cellspacing. Try this:

<table border="1" cellspacing="0" cellpadding="0">
    <tr>
        <td>1. This row will be displayed.</td>
        <td></td>
    </tr>
    <tr>
        <td></td>
        <td>2. This row will be displayed.</td>
    </tr>
    </tr>
        <td><!-- 3. This row will not be displayed. --></td>
        <td></td>
    </tr>
    <tr>
        <td>4. This row will</td>
        <td>be displayed.</td>
    <tr>
</table>

I'd go with AMPScript. Something like this:

%%[/* Modify to view AMPScript <div style="display:none"> */

var @r1c1, @r1c2, @r2c1, @r2c2, @r3c1, @r3c2
set @r1c1 = "r1c1"
set @r1c2 = "r1c2"
set @r2c1 = "r2c1"
set @r3c2 = "r3c2"
set @r3c1 = "r3c1"
set @r3c2 = "r3c2"

/*</div>*/
]%%
<table border="1">
    <tr>
        <td>%%=v(@r1c1)=%%</td>
        <td>%%=v(@r1c2)=%%</td>
    </tr>

    %%[ if not empty(@r2c1) or not empty(@r2c2) then ]%%
    <tr>
        <td>%%=v(@r2c1)=%%</td>
        <td>%%=v(@r2c2)=%%</td>
    </tr>
    %%[ endif ]%%    

    %%[ if not empty(@r3c1) or not empty(@r3c2) then ]%%
    <tr>
        <td>%%=v(@r3c1)=%%</td>
        <td>%%=v(@r3c2)=%%</td>
    </tr>
    %%[ endif ]%%  

</table>

Reference

• if
• empty()