Ampscript is definitely much faster for some things. I have seen improved rendering time just grabbing a value directly using Ampscript. However, if you're performing comparison logic on just one field from a data extension and want to use SSJS, it probably doesn't hurt you. I use it all the time.
Pulling data into a data extension is easy.
Step 1 - Setup your AMPSCRIPT and JS variables.
<!-- AMPSCRIPT VARIABLES -->
<span style="display:none;">%%[ var @TITLE, @PassedInTITLE ]%%</span>
Then, Setup your SSJS
var TITLE = Attribute.GetValue("TITLE");
Step 2 - Capture the
SET @PassedInTITLE = @TITLE
Step 3 - Now you can output the value of your Ampscript variable.
However, if you're doing working with Strings in your SSJS you'll need to remove the double quotes from your SSJS variables in Ampscript like after the stringify step and just prior to outputting the value.
SET @PassedInTITLE = Substring(@TITLE,2, Subtract(Length(@TITLE),2))
Your email won't render instanteously in preview mode but it won't take forever either. I do this all the time with multi-dimensional arrays in SSJS.
One thing though...watchout for leading and trailing whitespace that might exist in your data extension data. It's so much easier to utilize ampscript's trim function (i.e.) TRIM([TITLE]) - than to create a custom trim function in SSJS. So your code may look like this if you need to remove unwanted whitespace found in the column. Doing that in SSJS will slow rendering and load speed.
SET @PassedInTITLE = TRIM(@TITLE)