I'll say this now I have only tried two different felt liners so this review is only on those two.
The two liners I have been using are Collection 2000 Extreme 24 Hour Felt Tip Liner (£2.99) and B. Dramatic | Bold Liquid Eyeliner (£5.99)
(I've had the Extreme liner long that's why it looks a little tatty)
There's very little difference in the size of the tips but I think the Extreme Liner (right) is just a little chunkier.
When swatched you can see that the Extreme Liner is much darker than the B. Dramatic liner and therefore gives a more polished look.
B. Dramatic Eyeliner
Out of the 2 I much prefer the Extreme Liner. I find with the B. Dramatic Eyeliner I have to go over my line a few times to get a darker look, where as the Extreme Liner I don't, one sweep and we are looking good. I would definitely repurchased the Extreme Liner and its only £2.99 and lasts quite well.
The Extreme Liner comes in 4 colours Black, Blue, Purple and Teal. I also own the Teal one which I will swatch and show soon on this post. One thing to notice though with the Teal colour is that it is harder to get off the lid. The first time I used it I still had a blue 'tattoo' left on my lid the day after.
Hope this helps!
Thanks for reading!