it basically depends on the service requirement and also proportional to traffic or the size of the lan which you have in locations.
In my SP environments its mostly the E1 links which gets connected to the CE.
May be the other variant whichs T1 being used in NA and some other geographical locations.
As far as encapsulation is concerned its better to leave as it to default which HDLC untill unless if you are conencting to a non-cisco device wherein you need PPP to be coded in there.
ppp you can have if you want to have a multilink bundle which is logically bundling 2 physical interface and make use of the resultant value of the b/w of those physical interfaces(easy way to have load balancing but difficult to manage or monitor the physical links coz the ip reachability will be only for the multilink interface and not to the physical interface)
if its a small group of organisation and their work basically doesnt require all the 24Hrs connectivity they can very well opt for ISDN too..
Peopl who have enough requirements and who all are very much reduandant concerned they have both flavours like E1 or T1 as their primary and ISDN as their backup.
If you take a SP to SP scenario for uplink interconnectivity purpose they talk in OC-3 ,OC-12 or even OC-48..
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...