A CE4 is a disposable unit. A CE5 has a replaceable wick/head/coil. Both have a wick, but in one you can replace it rather than bin the whole thing.
I wouldn't touch the CE4s (having used them for a long time, and got to know them pretty darn well) The CE5 versions are much easier to clean as well as having the replaceable wick/head/coil. (If you are so inclined DIY rewickable, though if you are like me you will just buy replacement heads)
The iClear16s look the same as a normal CE5, but are a big improvement IMO.
I haven't tried the newest version of the T3s, but the ones I did try put me off them for life. The evods are a safe bet IMO, I have heard some mixed reviews on them, but the ones I have had have always behaved well. There are some clones around, I am 99% certain that mine aren't.
The only issue I have with the evods, the same as all BCCs (bottom coil clearomisers) is that the vapour is cooler even though there is plenty off it.
I prefer the vape from the iClear16s because it is warmer and more ... what I like ...
Having said that, an evod is much sturdier when droped, so I use both. iClears for at home and evods for out and about.
I recently got a mini davide for my aniseed juices, which is very similar(but better looking than) the mini protank 2. This produces clouds of vapour, but same as the evods I find it less satisfying because it is cooler/airier. (haven't dropped it yet, but think it would not like it )
I would suggest getting an iClear16 as well as a BCC and seeing which one suits you best
Bottom coils tend to wick better, and as the wick is always wet should last a tad longer too. Some people have problems with them, I suspect its because they are used to top coils that Work slightly differently. If you are flooding on a top coil then it often helps to do a couple of fast strong draws To clear the gurgle. If you try that with a bottom coil you will just make it worse. If you get gurgling with a bottom coil the best approach is a very light long draw.
For me, on a "normal" ego battery, I would get the 2.0 iClears.
You can sometimes find 2.2ohm evods, which are perfect IMO. I use 2.5ohm at the minute because I got 5 replacement heads with a kit I bought. They are ok ... 1.8 is too low for me without a VV battery.
At the end of the day it is personal preference, and depends what juices you are filling them with.
Don't worry .. after you have wasted a fortune finding what batteries you like, what attys you like and what liquids you like, and then bought spares for your spares in a rainbow of colours, the addiction does start to wane