Should we do hop on/off bus in London?

The hop on/off bus isn't not that effective of a way to get around London. The tube and busses will get you where you want to go more quickly. I wouldn't spend the time to actually do the hop on/off tour given your short visit. I didn't find it very interesting. Two days is so short for London. You don't say whether they are full days or include travel time. You will spend roughly half a day at both the Tower and Westminster Abbey. I suggest you get to these first thing in the morning. Peter Pan and Big Ben are things that take just a few minutes to see. St Pauls is interesting as are the British Museum and Library. There are also several good free art galleries. You can usually pick up tickets the same day for any plays and musicals except for the big hits. You could do this on either evening. You can get prices on the web for each attraction. 2 for 1 tickets need a train ticket for that day. I don't know how the system works. I've never used it.

If you have not been to London before, I think the hop-on hop-off is a good idea, but not necessarily as a way to get to your key sites. Most routes will include everything you mentioned (Wesminster Abbey, Tower of London and Big Ben). However, the hop-on bus is not an efficient way to move around. The tube is much better. There are tube stations that will let you out right next to Wesminster Abbey/Big Ben and the Tower. Instead, I suggest that you ride the hop-on bus for an overview of the city maybe as a late afternoon/early evening break your first day. You could also ride early to your one of your destinations (e.g. the Tower) and finish the tour later in the day. The buses start early and run late, so you'll be able to ride before many sites are open or after many have closed. This approach will give you a good feel for the city and some of its highlights. Pick one of the routes with a live guide. As for the places you mentioned, both have websites with pricing information and hours. You can also buy Tower and bus tickets in advance at this site (http://www.visitbritainshop.com/usa/?utm_medium=ppc&utm_source=google&utm_campaign=us_tourist). You'll get a printable voucher. It's not necessary, especially for the bus since there are brokers for the bus companies in multiple locations around town. I suggest that you try to arrive early for both Wesminster and the Tower, especially the Tower. It will get crowded by late morning and there will be a line to visit the crown jewels. If you can pay cash, the cash line at Westminster moves faster than the credit card line. If you're looking for ideas for shows/musicals, I saw the Lion King at the Lyceum with my familiy earlier this month and highly recommend it. You can also eat and check out Covent Garden nearby. There is also a free evensong service at Westminster Abbey both of the days that you'll be in London. Good luck

You will definitely have time to see the sites you listed and, with a bit of planning fit in a few more! HOHO buses aren't the most efficient way to get around, but given you only have two days,would work out well for one of the days and allow you to get an overview of most of the sights. As the previous poster stated, use it to get to either Westminster Abbey or the Tower as you definitely want to do those first thing in the morning as they get busy!! As for the 2 for 1 tickets, you can print off vouchers for these before leaving the states. In order for the voucher to be valid, you need to have a 1 day or 7 day Travelcard purchased from the National Rail System - this is a paper card good for travel on the metro, buses and (I believe light rail). Given your short time in London and the fact that you the only sight you listed that has has an admission charge is the Tower, I'd skip this step. Couple of thoughts - for Westminster Abbey I recommend the Verger tour - which does cost money but is well worth it. The Verger tour gives you a wonderful overview of the Abbey's history and lasts a bit over an hour if memory serves me correctly. As for show tickets, definitely recommend taking in a show one evening. You can buy tickets before you leave (full price) or you can head to Leicester Square in London where there are several ticket companies that sell discounted tickets. Lastly, for a decent sandwich on the run, pop into any of the Pret a Manger shops in London. Their sandwiches are pretty good and not that expensive.
Have a great trip!!!

We really enjoy riding the HOHO busses everywhere we go, even here in SF where we live. But as others have said, I would not use one for transportation. They're a nice break from walking, and a fun way to see a city if you sit up top.

Just yesterday I went past a couple of those sights on an ordinary number 148 bus. I got on near the London Eye, went across Westminster Bridge with a lovely view of Big Ben, around Parliament Square and Westminster Abbey, then on past Victoria, along the back of Buckingham Palace Gardens to Hyde Park Corner, then up Park Lane to Marble Arch and along the northern edge of Hyde Park, where I got off at Lancaster Gate. I had a London travelcard included with my train ticket, but with an Oyster card that would have cost £1.40. Rather than going to my departmental conference at a large hotel I could have wandered down through Hyde Park and Kensington Gardens, seen the Peter Pan statue, then carried on to Palace Gate in the south west corner of the Gardens and caught the number 9 bus (having waited for one of the old Routemasters with the open platform at the back which operate on that route) to Trafalgar Square and changed to a number 15 which would have taken me past the Royal Courts of Justice, Ludgate and St. Paul's Cathedral and on to the Tower of London (and once past Aldgate it's a very different side to London that most tourists probably don't see). Of course I could have broken my journey anywhere I wanted and known that another bus would be along in no more than 10 or 15 minutes and usually less. Each new bus would add £1.40 to the cost, but Oyster has a daily price cap of £4.40 if you only use buses and trams, no matter how many times you change. By the way, I saw lots of the brand new Routemaster with the open platform operating on route 24.

We were in London for 2 days in July and it was our first time. The Hop-on-off tours you can use the pass for 24 hours. I was glad we bought it,
as a first timer. It gives you a sense of the city, where things are. You have the freedom of getting off. You don't have the worry of oyster cards and am I taking the right connection. You are above the city and can see the sights and take pictures. If you start early the first day you have enough time to see all that you mentioned. The Abbey will take a few hours rushing, also the same with the Tower. Yes there is alot to see at both places. Big Ben Peter Pan statue-just photo shots.