Contains is a superset of Starts With.
If the expression is always anchored at the beginning, use Starts With. This will also cut down on false positives where "ibu-bbe" accidentally appears elsewhere (remember, Marketo doesn't stop that string of characters from being in another position, it's on you to make it have special meaning).
You're better off using 'Starts with', since the phrase is always at the beginning for your programs.
If you use Not contains, it will exclude all programs which has IBU-BBE in start/middle or end of the program name. (for example, 2017_IBU-BBE01_Autoreponse would be excluded too).