[Closed] Hotwater cylinder, worth changing from vented to unvented?

Imminent boiler replacement may result in having to replace the hot water tank. Might as well get one with a solar coil in it since I will install a themal system later on this year. So, I have two options:

1. Stay with the traditional vented cylinder with a cold water tank in the roof.

2. Change to an unvented mains pressure system.

Is there any point in going to the extra expense of a unvented system? I already have a pump for the shower which would be nice to get rid of but there is no guarantee that the mains pressure will be as good. Roof space isn't an issue either for the cold water tank. Are unvented systems better or more efficent?