To be honest, i've never used EntLib but have looked at it, so know a little about it. As far as i know, EntLib returns typed datasets, rather than having a BLL with the ActiveRecord pattern. Based on this assumption, the key strength of TBH is the fact that you can model your domain (BLL) in a heirarchical fashion with all related parent and child objects. you can also lazy load entire entities and/or individual properties when you have complete control of your domain model.
Also, as TBH uses the provider model, your datastore can be anything from a database to an XML file to a spreadsheet, etc, etc. All that you require to do is 'write' a provider for this in the DAL namespace and your BLL layer will function against that with no changes required. In EntLib (from what i've read) it's limited to SQLServer/Oracle databases etc...
Obviously, an indepth study would reveal further differences and one approach may suit you more than the other. However, in my opinion, as TBH is a totally patterns and practices based model it shouldn't be too difficult to move from one model to another, just more an issue of deciding what fits your requirement up front. If typed datasets is your bag, then EntLib would be a no-brainer. If however, you need the further flexibility to express your domain more richly, then i think you'd have to consider TBH (or nHibernate etc).
just my thoughts based on very 'slim' knowledge of EntLib.