Wow :O I had to try it just to check it out, you're right it's totally a flavor killer, why... why?!?! some people choose to use it?
Is there any other flavor booster or sweetener other than sucralose? preferably something that won't lose taste after few weeks?
I'm tasting my liquids and going back to vape branded eliquids I purchased in the past, it's really disappointing, how can I reach the amount/strength of flavor that provided by "shelf" eliquids?
People often use EM because they read somewhere that it sweetens, and they haven't done the comparison you just did! It is useful sometimes to mute flavors. Imagine you're making a smooth, creamy lime pie recipe, and the lime you're using has a bitter zest flavor - EM would mute that.
In my opinion, the key to good recipes is starting with great flavors, finding your personal ideal percentage for each as a standalone flavor, and lots of experimenting with combinations. If you can find recipes to copy here, ones you really like, then you'll often like others by that same person. If you want to be able to make your own creations, there's just no way to avoid experimenting. I think it's fun!
Stronger flavor... using your Reese's as a starting point...I suggested starting at 3% Double Choc + 2% Peanut Butter. So you try that and ask yourself how the balance of choc/pb is. If (for example) the pb flavor is too prominent, you add a little more chocolate. Say you end up with 4% Choc and 2% PB. But it's just not strong enough. Then you increase both flavors using the same ratio. Your 4:2 Choc

B would go to 6:3 next. Still not strong enough, try 8:4, then 10:5... Try in small steps like that, because if you overshoot it, it can taste just horrible.
Continuing the same example, let's say you decide 8% Choc with 4% PB is the right balance of the two flavors, and about the right strength, but still missing something. That's where the real experimenting begins. I really recommend using other sweet flavors instead of Sucralose or any other sweetener. It'll taste better and stay tasty longer. For candy flavors, try adding a little marshmallow and/or caramel instead of sweetener. If you'll be adding more than just a tiny bit, mix a little batch of weaker recipe to add to - like 6:3, which leaves room for some other flavoring without getting too strong. You might still want a little Sucralose, but adding those sweeter flavors will at least minimize the Sucralose. (all the sweeteners have their own weird aftertastes if used excessively)
Regarding steeping... You'll find a lot of strong opinions here on whether it's necessary and what equipment to use for how long. I'll just be blunt - why bother with it! I vape fresh. With the exception of spicy flavors and tobaccos, I make my mix, set the closed bottle in hot tap water for a few minutes (makes the liquid really thin), shake it really well by hand, then a few more times as it cools. Always give it another quick shake before you use it. I make lots of dessert, coffee, candy, fruit, and other recipes (not many tobacco) - some with many different flavorings - and I do not age anything longer than overnight. Why not try it that way! - sure saves me the frustration of waiting, and my recipes taste great to me and most who try them.
Regarding great flavorings... different people have different preferences, and each flavor brand has its superstar flavors. There's just no way to know which ones you'll like without trying them yourself as standalone flavors. It takes time, I know. You can minimize the expense by buying small samples first. Bullcityvapor and purevapes have very cheap sample sizes, less than even wizardlabs, onestopshop, and rtsvapes.
We've come up with some super-tasty recipes using all/mostly FlavourArt flavorings over here:
http://www.e-cigarette-forum.com/fo...pure-vapes-has-3ml-flavourart-flavorings.html It's a long thread, but full of tips, flavor descriptions, recipes, and ideas. There are similar threads for TFA and other brands. I have a huge flavor collection, but FA are my most-used.