Many operators favor flaps 25 landings (even to the point of making it the standard landing flapsetting) because of fuel savings and noise reduction during the approach. However, as a crew you need to factor in all variables that may be relevant (such as runway length, head/tailwind, runway condition, landing weight, minimum runway occupancy time, resulting brake temperatures) and if you think flaps 30 would be the better/safer choice, then flaps 30 it is. As long as you are below max landing weight either flaps 25 or 30 is fine, based on your judgement of the mentioned factors. One is not more difficult than the other, just get familiar with the slight handling (flare) differences.
If you need to make an overweight landing, you may not be able to use flaps 30 because your approach speed is higher than the flaps 30 placard speed. The OVERWEIGHT LANDING procedure will give you guidance here, but it may be a good idea to have an idea of the weight above which you will need to use flaps 25 (or possibly flaps 20 if you have an engine out).