Going with the higher ranking professor will usually ensure that you have money and expert guidance in your research but in most cases the professor simply won't have that much time for you. He is also unlikely to participate in your lab work at all but will usually allocate someone to help you out (or not). The professor is likely to have quite a few students doing his research so you need to work hard to earn his attention. It also means that if you are not doing well in your research, he can afford to lose you because you really are expendable and he has others who can earn him publications.

The senior lecturer is presumably less busy although, some lecturers have heavy teaching loads. They probably have less research funding but they should be alright. Because they are not that high in the sky yet, some actually teach you first hand in the lab or even run experiments themselves. They will also likely be able to spend more time with you and give you slightly more attention. If you are your lecturer's only student or one of a few... he will definitely do what he can to help you out if you're struggling because he needs you to succeed so that he can publish.

Don't forget this is generalisation but that's because there isn't any other information apart from the 'titles'.

This post has been edited by Farmer_C: May 16 2013, 06:09 PM