Yo yo yo....
Like many people have said, a large part of what instrument and string type you want depend on what sound your looking for. I play fairly hard rock and do lots of finger tapping and active melodic bass lines, what people seem to like to call "lead bass" and after playing many different types of basses I setteled into an american made Fender P-Bass and it has stayed my favorite. I played part time for a few years on a Peavey and it was pretty good but I preffered the Fender. I did get a Peavey fretless in a good buy and it has been a good addition to my arsenal. Alembic's have a very unique sound which can be good and bad at the same time....no matter what I added to that sound it always sounded like an Alembic. Yamaha has a nice line, and Music Man does as well although I havn't played one personally. I would say until you have at least $700 bucks to invest (unless it's used), stick with what you have and save. Buy American and you will get quality....it's a HUGE step up from the mexi/korean/taiwan models of any line.
Strings really are a personal choice and believe it or not, they are not all made the same. I would suggest each time you buy new strings try a new brand until you have covered these:
GHS Boomers: My personal favorite! They are very live and have a real nice high end sound.
Ernie Balls : My old band won the quarterfinals of their International battle of the bands back in '98. In addition to going to the semi's and getting to play on the Van's Warped Tour when they came here, I got about $500 worth of their bass strings. I still have some left because I prefer the boomers so I use them when I want new strings on but don't have a gig coming up. They are very similar to the boomers, but I swear the E string isn't as live when I tune to drop D.
Fender stock: I don't like 'em, but others swear by them.
Okay, maybe someone can help me...don't know the brand name but there is a lion on the front. They cost like $45 instead of $22 but they are supposed to hold the high end longer than normal strings ala Elixers for guitar(it's not Elixer's is it guys?)
D'Addario: sounds like you already tried them. Pretty good all around, I think the Boomers are brighter though so ....
Anyhow, hope this get's you started. Just keep plugging at it and don't let the guitar players give you crap. Good guitar players are a dime a dozen. Good bass players are hard to find
