I like the silicon softips better than foamies or flanges. Flanges are really hit or miss. You either like how they fit or it feels like you're inserting thistles into your ears. Foamies are a bit more forgiving, but I always feel like I'm stuffing cotton in my ears when I try to use them. Softips have a light touch and with a good fitting IEM (Shure SE, Westone, etc.) they can easily 'disappear' in your ears - you forget about 'em and concentrate on the music. They clean easily, wiped down with a soft cloth and water or mild cleaner, and are very reusable.
I simply press them into my ears until I get a seal and they feel comfortable - that's the right spot (A bit more complex with the UM2s as you also have to position the driver 'kidney' for comfort while also positioning the nozzle for optimum aim which gives max treble, etc. but with practice it's all a press into the ear.). When freshly cleaned they will remain in place for pretty much as long as I leave them there (usually 2-3 hrs. but as long as 5-6). In my Etys, I use mediums - the Etys insert moderately deep into the canal. My UM2s I use Large - they don't insert as deeply so I need a larger tip for a good seal. As well as these work for me others can't stand 'em, so go figure. Like all tips, it's all about the seal, so make sure you get all sizes to try with your IEM; as above, different IEMs might need different size tips for a good seal. BTW I use the Shure tips as they're pretty much universal fit for Shure, Ety, Westone, and others. A bit pricey, but then again 2 years and still on the original pack of 5 pair. Good luck.
