Buy whichever bass feels best and easiest for you to play. The most important thing for a first timer is to have a bass you like and want to pick up and play. Don't buy an instrument because it looks nice, or other people say it's great (it may be great for them, may not be right for you!).
Once you've found a bass which feels right, then you look at strings: stainless steel roundwounds are bright, zingy, sometimes metallic sounding. Nickel roundwounds have some brightness, but are more 'bassy' sounding, warmer and a little easier on the fingers.
Pickups should be secondary to both the above. You basically get two types of pickups, vintage or modern. Once you are proficient enough, you can get loads of suggestions and advice on pickups on this forum, or do a search, and read for yourself.
Fenders, Sires are good, but may I also suggest Yamaha TRBX or BB range basses, they are excellently built, sound good, and have super nice necks, making them very easy to play and feel very nice in the hands.