Hi Edvinia,
As far as myself is concerned, i would say both are having it's own advantages and disadvantages.
SAP Basis,
I do love doing tasks related to SAP Basis which looks like Herculean task sometimes and will learn many things out of it. We need to have knowledge in OS, Database, Network to excel as a good SAP Basis consultant.
If you don't worry about work life balance then you can go for SAP Basis.
SAP Security,
Even though SAP security looks very simple to learn when it comes for a mass activities, we would need to use our mind. For Example, Creating 1000+users using scripts, changing 100+ roles using scripts, LSMW.
You can keep all the security stuffs which you have learned with you and start exploring Basis.
All the best!!!
Regards,
Jegan Raj