Ultrawide is good but not all games support it officially, have to use some mods or tweaks to make it work, if not you gonna game with black border at the side 

Just using DELL S2340L now.

I'll help U out to sum up the difference of DELL U2913WM vs LG29UM57 since I pretty much did this when I started choosing myself.

1: Much more connectivity options. (LG only uses HDMI)
2. Higher max brightness.
3. Swivel-able stand.
4. Built-in USB hub.
5. Audio out-put.
6. Better warranty(?) (DELL promised 1 to 1 screen exchange even if only 1 bright pixel is found)
7. Better looking overall when the monitor is not powered on. [ LG is very close with this, also features a virtually borderless design (overall looks the same as the DELL) ]

However, there is also a few disadvantage against the LG:

1. 8ms respond time compared to 5ms.
2. Costs a little more than 50% more money.
3. LG's monitor control uses a analog stick like the ones on ps4/xbox controllers, it is very easy to navigate thru monitor settings. (I didn't check DELL's but I'd assume DELL is using plain o buttons)

Mutual stuff to note:
1. If U're unlucky U may receive a terrible light bleed product (I read more review on DELL having serious lightbleed issues)
2. Both are able to overclock to 75Hz refresh rate+- (LG only goes to 75Hz max ; DELL users have reported to be able to overclock it a few more Hz stable)
3. These monitors are long if U didn't already notice. Needs more space on the desk compare to 16:9 monitors. U should measure before buying if U're working in a tight space.
4. Might not scale well with unsupported games. (though usually people have already created a mod for that for most games)
5. Both features anti-glare screen.

That's pretty much it, I might have left out a few.

Although I'd like the DELL to match with my current DELL, but I don't want to spend +50% just for that, and LG has higher respond rate.

yes i bought,

tl;dr

so far so good, my 1st 21:9 monitor, i can definitely recommend this aspect ratio to everyone.

Will give the long version after my dinner.