You have 45 minutes to ride and need to be back at the same door. A short local loop and an out-and-back can both fit. They give you different ways to change the plan once you are moving.
Start by deciding how much flexibility you need.
On an out-and-back, you follow a route away from home, then retrace it. You can turn earlier than planned, but every outward kilometre adds a return journey. Halfway through your available time is not automatically the right turning point: a downhill or tailwind on the way out can leave a slower trip home.
Choose this shape when you want to reach a particular stretch of road or trail and have a realistic allowance for getting back. Set a latest turnaround time that leaves a margin for delays.
A short loop brings you back to the start at the end of each lap. If it begins close to home, you can decide there whether to finish or go round again. This suits a ride whose duration may need to change, because the next decision happens near your exit.
A big circuit does not offer the same flexibility. Being halfway round a 30-kilometre loop can still leave a long journey home. Check where you could shorten it before committing to the full circuit.
Map shape is only one filter. A neat loop with awkward crossings may be a worse choice than a familiar out-and-back. Look at the surface, junctions, climbing and likely conditions before settling on either.
Count the ride to and from the loop as part of your available time. If reaching it uses most of your window, the local circuit has lost its advantage. Another lap also needs a full lap's allowance, even when the start feels close.
When timing is tight, I would choose a familiar short loop with a clear way home. When there is room to explore, an out-and-back may suit the day better. Choose the route that lets you finish the ride you intended, without a rushed return.