I've been using Opera since just about the beginning and I still use it, almost exclusively, because it does almost everything I need and it is the fastest browser out there. I also like Firefox because it does have a plug-in structure that provides some capabilities Opera does not easily accommodate.
Opera appears to be the only browser that adheres strictly to html standards and that is, in a sense, its only flaw since a few websites opt to design their pages strictly for MSIE which does not adhere to the standards. On those rare occasions when Opera chokes on a website it's easy to fire up MSIE or (preferably) Firefox.
In any case, why don't you just go ahead and use Opera since it is free! Not only that, it is still under very active development and version 9 should be coming out fairly soon. It's almost guaranteed to be around for a good long time if Google does pick it up.