Should I rather be shooting 1080/50i or 720/50p for 25fps web use?
If you're mainly concerned about the staircasing, consider where the video will be watched. If interlaced video is shown on a display made for interlaced video, it appears ok. If you play it on a progressive display (such as a computer monitor) the staircasing is easily noticeable even for little horizontal movements (of the camera or of the subjects). For details see https://cardinalpeak.com/blog/interlaced-video-and-computer-monitors/

Best is if you never have to deal with interlaced video if possible.