Latoken has a lot that is needed both for projects and users. They are known and work good for traders, have one of the fastest support and 0,1% commissions on the majority of pairs I trade, which is comparably low. Btw Latoken has never been hacked and their IEO launchpad contains more info on the projects listed than most other exchanges' ones do.
Otherwise, can't share the detailed opinion on P2PB2B. Can say that they are much slower.

We should remember that success of an IEO depends on the project.