Neither for me. Once I put in an SD card, I really have no need to take it out. Any convenience is offset by the security concerns I have if I lost the phone. With internal memory, there is some security protection which would at least delay the access and give the owner the chance to do a remote wipe. With a removable SD, all the information may be accessed immediately.
I appreciate that some power users who have no access to charging during the day have an absolute need for extra batteries. Personally, I would find it more inconvenient to carry an extra battery and have to go through the hassles of pulling and charging more than one battery. Do external battery chargers exist anymore? I remember about 20 years ago, I would have an extra battery in a charger while a fresh one was in the phone (but then 12 hours standby and 60 minutes talk time on NiCads was the advertised battery power). If you have to charge the extra battery in the phone, isn't that a major inconvenience? I have just modified my behaviour so that I never have to charge more than once a day (usually end of day over night).
My Shine Plus has a stainless steel cover with a nice locking mechanism. It opens easily and has not shown any wear (considering the number of battery pulls to reset the dam thing). On the other hand, my son's Optimus One has a plastic clip on cover. Fortunately, he has not had to do any battery pulls. But I would be concerned that opening and closing it will eventually wear out or break the clips.