Im no SMT expert by any means, the two games your considering are the only two I've played myself but I enjoyed SMT IV much more. To be honest i spent about 40 hours on SMT IV compared to only 6-7 with overclocked, it just didn't get me hooked but I know it's a long game with lots of content.
The tone of each game is somewhat different, overclocked story, characters and dialog feel more anime like (not tales series though) while SMT IV is a little darker and more serious. Both deal with demons and death though so don't expect anything happy.
The main difference is gameplay, overclocked is a grid based strategy and SMT IV is like a dungeon crawler. Each one has basically the same battle system, its all about having a diverse roster of demons with different strengths and weaknesses.







