Transportation between Shenzhen and Guangzhou is easy, and there’s two main options via public transport. The first is by train which I recommend over the buses. Travel time is approximately 1 hour via train and 2 hours via bus.
Trains leave from Shenzhen Railway station which is down the block from the Hong Kong LoWu Border, making it a quick 5 minute walk if you’re coming from HK. There’s a ticket office on the left side of the building on the ground level, only selling tickets to Guangzhou. Tickets are 80 RMB each way. Trains leave approximately every 10-15 minutes to Guangzhou East station, there are less frequent trains to Guangzhou station. Depending on your final destination, it may be better to wait for the next train to Guangzhou rather than going to Guangzhou East, since GZ East is still a bit far out.
The high speed trains are relatively new, quiet, and travel very quickly. It’s a bit of a cattle call when they board the train but there’s assigned seating, even though you’ll probably have to kick someone out of your seat since people tend not to always honor the assigned seating. I don’t think you need to buy tickets in advance unless it’s a major holiday like Chinese New Year or National Week. This is the easiest, fastest, stress free way to get between the Shenzhen and Guangzhou.
There’s actually a new line which opened on December 26, 2012, Guangzhou South connecting to Shenzhen North. This will be part of the Express Rail link through Hong Kong. However, it’s not convenient for HK travelers and I’ve never taken it so can’t comment too much about it. I did read fares are 100 RMB.
Buses will be cheaper than the train, I don’t know the exact cost, but I assume about 30-40 RMB. Buses in Shenzhen leave primarily from the border terminals with Hong Kong.
Luohu Coach Station 深圳罗湖汽车站
Futian Coach Station 福田汽车站
Shenzhen Huanggang Border 皇崗口岸入境大堂
Nanshan Bus Station 深圳市南山汽车客运站
Guangyuan Coach Station 广州广园汽车站
Guangzhou Province Coach Station (Next to Guangzhou Train Station) 广东省汽车站
China Hotel 中國大酒店
I don’t recommend the buses because the drivers drive like maniacs, constantly switching lanes, honking, etc. It’s just an unsafe, bumpy, and unpleasant ride. The quality of the bus should be fine, a normal coach bus, so no concerns with the seating if you do decide to take it.