psychbio is universally known as the "easy premed major." it has a wide range of classes, from pretty much every science department, including psych (that's a science dept at ucla), mcdb, mimg, neuro, physci, biochem etc.. (pretty much everything)... so i guess supposedly that diffuses the whole "premed competition" thing...
physci has a reputation for being hard. i was told that neuro and physci are the two hardest, but others dispute that and say mimg is also hard... in any case,all that is important is that they are "hard" but in my opinion, you should study what you love and not let anything stop you. supposedly neuro is a more welcoming community because there's a neuro undergrad society...
my advice is that you should wait until you take your lower division LS classes to decide. all life science (i.e. "premed") majors have the same lower div requirements (those you will normally take your first two years), including a completion of calculus and a year of chem, physics, and LS. (neuro also requires one quarter of stats, but other than that, they're pretty much the same). all the LS classes each pertain to one LS major. LS1 (ecology, evolutionary biology) is the EEB major (ecology and evolutionary biology), LS2 (cells, tissues, and organs) is the physci major, and LS3 (molecular bio) is mcdb, and i 'think' LS4 (genetics) is MIMG. If you take psych 10 (intro psych), they also cover some neuroscience in that class, as does LS2. so you don't really have to decide until you finish all the prereqs, since they're the same for all the majors anyway. then you can pick and choose what is your favorite subject to study.
in my opinion, i think you are most successful doing what you love. i was going to do psychbio, until i took psych 10 and found out that i hated psychology and wanted to do more laboratory-oriented hard science. so i switched to neuro and am working in a neuro lab. and i love every minute of it. when you pursue your passion, your increased level of motivation opens up a lot of doors. had i stayed in psychbio, i wouldn't have tried as hard to find as many opportunities, just because i wouldn't have been as excited. in the end i think you should always live your life to do what you love. but thats just my philosophy. anyway...