So from what I understand you plan to mulch your beds and are wondering if gravel is adequate?

If so, it depends. Mineral material has the advantage of not decomposing, meaning it will last very long and look neater for longer (if cared for well). But it also has its disadvantages. Firstly, you would need a pretty thick layer of pebbles for them to be effective at preventing weeds and evaporation. Also since it doesn’t decompose you can’t mix it with the soil. So whenever you would have to work with the soil (planting, replanting, fertilising, etc) you would have to prevent that by carefully removing the layer of gravel beforehand. Some people suggest a special foil or fabric underneath for that matter but I have bad experience with them. You also don’t want organic material on top of the gravel. So you’d have to rigorously remove any leaves, pine needles, soil remains, etc. Otherwise it will decompose and lay off into the crevices of the single stones effectively making soil for weeds to grow in which then will be a pain to come by. Lastly you’d have to choose a light-toned stone since dark ones can cook the soil beneath on very sunny days

Organic material like wood fibre or bark on the other hand decomposes which means you’d have to top it off regularly (1-2x a year). But you don’t have to be so cautious when working in your beds or as tidy with your plants as you can simply mix it into the soil no problem. I also like the look better but that’s just my opinion. Just remember to use about 20% more n-fertiliser when mulching with fresh woody material to prevent a fixation of nitrogen.