Hi and welcome!
Prefilled carts are often filled with Dekang PG juice and some of the flavors don't have much flavor or aroma. You will find some tastier juices at many US juice mixers. like FreedomSmokeUSA and so many more. More complex flavors, various PG/VG ratios (some popular ratios are 70pg/30vg, 80pg/20vg and some like 50/50 - pg lets through more TH and flavor but is a bit harsh alone, and VG is smoother and thicker and adds vapor and a bit of sweetness but can mask flavors a bit.)
Gurgle is juice hitting the atty - it can do that. If the atty stops vaporizing well though, unscrew and remove the cart and make sure atty isn't flooded (blow out into a tissue).
Drip tip can only be used really safely on manual batteries with no hole in the middle of the threaded end of the battery (because you don't want to get juice inside the battery). It's a wide-hole mouthpiece (steel or aluminum ones work best I think) that you attach directly to the atty (no cart). Then you can drip 2-3 drops of fluid in the mouth-hole of it, puff in lightly to get the juice to go down, then vape for a bit. If the vapor gets light, add another 1-2 drops. Not good to do when driving!
And - for when your cart white stuffing gets buggy and not wicking well, I recommend replacing the white stuffing with blue foam. Strictlyejuice.com sells some really cheap precut pieces for 510/901. Then if you like the blue foam and are ready to cut your own, but the uncut foam and Marineland Rite-size U Foam Sleeve in the aquarium dept of Petsmart (was out of stock at mine for a while - I wonder why haha)
Some maintenance things I recommend
1. Clean your atty once a week - I soak mine overnight in vodka (grain alcohol like Everclear would be purer while still edible). I make sure it is submerged with no air bubbles in a small jar of vodka, swish it around a bit, leave overnight. Next day I remove it and shake it out really well and lay to dry. (I alternate two attys - one I am using and one I am cleaning). if you need the atty right away, dry with paper towel gently and blow through it until it's dry.
2. Whenever you are about to screw a battery into a charger, wipe off/out the threaded end of the battery to make sure there is no juice on it. You don't want to get juice in your charger socket - even a thin film of dried juice can make it harder to charge a battery, and a buildup of juice in the charger socket would be worse.
3. Pay attention to the heat of your atty especially if you are not getting good vapor - if it's super hot then it's not getting enough juice so check the cart, adjust the filling, top off with juice - whatever it needs, because running an atty super hot could shorten its lifespan.
And wow - favorite juices - that really depends on the person. I think Turkish tobacco blends seem popular as well as flue cured tobaccos and 555 (vanilla almond tobacco) and RY4 (vanilla caramel tobacco). Chocolate flavors are nice (especially since so many cigarettes have cocoa in their ingredients). Some like liquor flavors or spicy or fruity flavors.
I can only use fruity foody flavors brief fun vapes or as as additions to tobacco juice - I can't do fruity/foody all the time because I don't feel satisfied and instead feel like I ate. Some other people can vape foody/foody vapes all day.
My faves so far - Backwoods Brew Casablanca and their amazing Peach, FreedomSmokeUSA Desert Ship which I sometimes add a bit of their Chocolate or their oRYental to (a light RY4). Velvet Vapors Raspberry Gingerale (tingly TH), AveJuice Boba's Bounty (all VG but so amazing for VG) for those times when you need huge vapor and a TH that will leave your throat burning. For adding to other tobaccos I also like Velvet Vapors Vanilla Almond Tobacco (their sweet smooth version of 555). And Gourmet Vapor where you can mix your own blends online, and their juices also have a ton of flavor - this is my own spiked eggnog ejuice which came out decent so I made it public.
http://www.gourmetvapor.com/flavor.php?flav=3458&show=8&q=eggnog