I just got back from my second trip to Guatemala and thought I'd share some tips. I traveled with a friend, both females in our late 20s.
We chose to stay at the Black Cat hostel this time. Last time, we stayed at Jungle Party and at Kafka. None of these hostels are amazing, but Black Cat has the best social scene and breakfast. The bathrooms could use some work.
Jungle Party has a bad layout, bad breakfast, whatever staff, and is pretty run down overall. Its best feature is the common area.
Kafka is a bit better in terms of staff and layout, but the rooms and beds could be improved.
Yellow House is definitely the best hostel option in Antigua. The dorm room has regular beds, not bunk beds, and they have a computer for use. They also have a bunch of private rooms.
Yellow House also has the best prices for tours and shuttles. So if you're on a strict budget, buy your tickets here.
We took a shuttle to Semuc Champey for 120Q (prices vary up to 150Q). It took 8 hours. We chose to stay at Zephyr hostel there, which is the newest hostel about a year old with amazing 360 degree views and up the hill from the river. They have private rooms and dorm rooms, and scenic showers. The best food there are breakfasts (try the shake) and brick oven pizza. The staff was amazing and the tours were great. The caves and the pools full day tour costs 165Q with the hostel. You can do it on your own by payin 30Q for transportation from town and 50Q to get into each place. I would highly recommend to bring shoes that can get wet in the cave while you're walking and swimming in it. Otherwise, they have to tie your flip flops to your feet and it's not very comfortable.
Others stay at El Retiro, the older hostel in town that also gets decent reviews. Though Zephyr has been getting great feedback on TA reviews and through word of mouth and is often full. We got the last beds.
We then took the shuttle to Flores, which cost 75Q and took 8 hours. Pretty much everyone in town charges 60Q for transportation to Tikal. We used San Juan travel and I wouldn't recommend them for one thing: the guide insists on taking the $20 entrance fee in cash from you and you never see the tickets. We are sure they run a scam where they claim fewer people actually entered Tikal (we asked for actual tickets, which is when it became obvious). Don't give them the money and buy your ticket on your own at the ticket booth.
We also bought tickets to Belize City which takes 5 hours via the express bus (the bus drops you off at the ferry terminal if needed). We shopped around quite a bit and the best price for the morning express bus at 5am is 100Q via San Juan buses. The 7:30am buses and Maya buses are 110Q. Linea Dorada buses are more expensive. I would recommend Oscar at the Lavandaria/Ticket Office place on the main street for great service and prices without haggling.
Hope this helps!