Both are important.
Reading the NT only would be like watching a movie half way through.
You wouldn't understand the plot, the whys and wherefores, the twists and turns
or how the ending came about properly.
Reading the OT only and you won't get to the happy ever after.
Now here is something many people don't get. The story still has not finished,
it won't finish until the day you go to be with the Lord. Then the full story line will
be fully revealed. Doesn't that just blow your mind.
Each of us has the Old Testsment, the New Testament and our own personal Testimony.
Thats because God is not dead He is very much alive.
1 Corinthians 13:12-13 NLT
[12] Now we see things imperfectly, like puzzling reflections in a mirror, but then
we will see everything with perfect clarity. All that I know now is partial and incomplete,
but then I will know everything completely, just as God now knows me completely.
[13] Three things will last forever-faith, hope, and love-and the greatest of these is love.