If you need to be careful with the taxi drivers in Bratislava, be aware as you use the public transportation as well. The inspectors checking your tickets can from time to time be cruel, evil and trying to destroy your stay in Bratislava. Therefore, as you buy your ticket to the local transportation make sure to validate it immediately after entering the bus or tram. After leaving the bus/tram-stop the ticket validating machines are locked after half a minute, so be sure to validate your ticket at once.
15 and 60 minute tickets are available, but you should only buy the 15 minute ticket if you are sure to get of the bus on time.
The easiest and safest option is to buy a 1, 2, 3 or 7 day card for the Bratislava public transportation.