We will be in Vienna for 6 days and will be using trams and Ubahn to get around.
One of our questions is does Vienna City Card, for transport,which offers discounts on certain attractions let you bypass lines?
Does Flexi Pass allow you to bypass lines?
Is Vienna pass the only card that allows one to skip lines and just walk in?
Thanks in advance.
You can find the details for each type of pass here: https://city-card.wien-tickets.com/?ci=1&cm=23578801824_200270654344_t_g_vienna%20city%20card_e__kwd-308170826871&gad_source=1&gad_campaignid=23578801824&gbraid=0AAAAACRC4b1psLwEcz30WmIX3XnullnsI&gclid=Cj0KCQjw2t3VBhD8ARIsAK0F6qzcdgObaNsbImPV8iLdXLrcTj5UmCSnaB4Rde33pBcLwRHDDx5n5U4aAoB9EALw_wcB
The Vienna City Card does not pay off and you cannot bypass lines. But long lines aren't a problem in Vienna (except at tourist traps like Café Sacher, Café Central, Café Demel, Bitzinger sausage stand).
Better is to buy a regular public transport pass: https://www.wienerlinien.at/web/wl-en/tickets/7-days-vienna
The Vienna Pass does not pay off either. It does allow you to skip lines, although you won't find many. And it does not include public transport, meaning that you are confined to the Hop On/Hop Off busses, i.e., their routes and their schedules.
Upper Belvedere and Schönbrunn Palace are the only sights where buying time slot tickets would probably make sense. I am a walk-up guy and had never problems. Should your entry being delayed to a later time slot, there is always enough to see and to do in the meantime wherever you are.