70-528 for .net 2.0 ,and 70-562 for .net 3.5 .your question is equal to what technology is more suitable for you ,and or will give you a promising future.
3.5 is that it's only fully supported in VS2008 so you'll need to have a copy of that (or the VS2008 express editions) to make best use of it.besides .3.5 is the latest technology and
3.0 was that it provided windows presentation foundation, communication foundation, workflow foundation and cardspace, but that sits on top of the 2.0 framework.
.net 3.5 vs .net 2.0 exams just like server 2008 exams vs server 2003 exams or windows 7 exams vs vista exams .
The old technology is the foundation of the latest technolgy.
If you pass .net 2.0 exams or get .net 2.0 cert ,if it is necessary ,you can consider upgrade .net 2.0 cert to .net 3.5 certs ,which will be easier after your passing .net 2.0.
Besiders ,In my opinion,if you want to go to web-development in c# using asp.net ,you can consider .net 2.0 exams ,which more suitable for u.
Of course ,Niall's advise is also useful for u.you should consider about your working enviorment .
ps :your questions, to some extend, seems like to ask you which chewing gum tastes better: mint or lemon.however ,i have done my best to answer your questions ,hope it useful for u.
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