[arvydas]

There is no one answer for your question. Every lens you listed is good and with some limitations (including Sigma 17 - 70mm). BTW there is no such 15 - 50mm lens on Pentax land. Tamron and Pentax 16-45 are considered as having good performance/price ratio. Kit lens has the best performance/price ratio <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='' />. For low light fast prime/tripod/external flash might be more useful than even f2.8 zoom (at least you need zoom <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='' />).



A.