I would suggest that you would get the best results from the push ups as it is a great compound exercise, in my opinion better than dips and an isolated ab exercise, anyway.
The program is push ups, pull ups and squats. By all means do dips as well but I think you can gain a lot from struggling through a weaker exercise to over come it in the end.
For instance, I could not do pull ups for my first 4 months and substituted with body rows, but now, at my current level I am happily struggling with push ups.
Get stuck in and good luck!!