I have been using an X300 pretty much since the model came out.

Now I must choose a replacement.

I like the size and weight of the X300 very much and am afraid that the X1 might be too heavy. On the other hand, I like the 13.3" display too.

Would greatly appreciate your insights and advice here. Thanks in advance.

X1 is a monumental failure in almost every way. Look at the X220 and T420s and select which suits your requirements best.

Officially, the T410s and T420s are the successors to the X300 series.
But their battery life is not as long (you can get UltraBay batteries, however), and it's a pound heavier at stock.

I wouldn't get the X1 unless you're a big fan of glossy screens and chiclet keyboards...

There is no successor to the X301 class.
No 13.3 class thinkpad has come with regular keyboard, 1440 screen, 2 battery bays (Max 9 cell 6+3 modular) .
The x1, has 1 battery intigrate, 4 hours use.
The X220 has a potential 9 cell, but its big and ugly, and its a 12“ laptop with an low Res screen.

For this reason, I still use my X301 to this day. I've done may upgrades over the years to keep it relevent, most recent is a newer faster Kingston SSD.
With two batteries 6+3 cell the X301 can run for 12 hours straight. I've gone from Canada to Hong Kong with the laptop powered on the whole time.

We'll have to wait for the ivy bridge to see if the X3s make a comeback.

Ivy bridge release is soon (may in 3 months) so waiting makes some sense.

There is also rumors of 20th year anniversary model of thinkpad during fall 2012. It may be interesting to wait for the anniversary model and see if something special is offered.

X1 & X220 have HD LCDs (1366 x 768), 13.3" & 12.5", respectively. T420s has a 14.0" HD+ LCD (1600 x 900). I would base my decision on that alone.

In sticking with ThinkPads, I'd go with the T420s.

I go the other way. I say the difference between HD and HD+ resolution, about three lines on the a typical internet page, isn't really enough to sway me from giving up the better quality on the X220.

If by better quality you an IPS screen, then the x220 screen is not all its cracked up to be.
Personally I feel that the x220 LCD tend to be overtly warm, to the point where it almost feels like a panel defect. The X220 have some of the yellowist looking I PS panels on the planet. I had to run Spyder 4 on it to fix the yellow tint, even then it still leans towards a unhealthy yellow tint. So, really I'd prefer a normal LCD then a yellow IPS. Keep in mind this defect may be only for the X220t, since I've never owned a regular x220.

Second the X220, doesn't come with a GPU, so you're stuck with the Intel GPU, which is not that great.

Personally, I think the T420S is the best deal, assuming you pick up the Nvidia NVS with it. Also the T420s is the only think pad that supports extreme rapid boot, which can boot the laptop up in under 10 seconds. That's a feature I'd like to have.

The reds do skew a bit orangy on my X220, but I've never noticed any yellow tint to it. I think the average user isn't the type to calibrate their screens, but would judge the X220 LCD to be superior to what's offered on the T420s.

Nothing I do needs the GPU. For me I'll get the Intel and save the expense.

My X220 boots in just under 20 seconds on a clean install of Windows. I don't see an extra 10 seconds or so be worth all that much. If I want a fast boot, I'll get my R60e. Running Linux it boots in about seven seconds.

Yes, I meant orange tint, not yellow.
I thought it was just the x220t, so its on all the x220s.
What a shame. I never calibrate my laptop screens, this was the first time I ever felt compelled to run a hardware calibrator on an laptop LCD, because the color was so skewed from normal that I had no choice.

Also the X220 has no optical bay, the T420s does, just like the old X301.
Before you say that nobody uses an optical bay anymore, that's not the point.
The real reason why you always want an optical bay on a Think pad is the ability to swap it for a second battery or a second hard drive. Who doesn't need more battery and storage.

You are talking about two separate things. One is the bad calibration in the stock ICM profile that ships from Lenovo, the other is a lack of accuracy with reds. Fixing the warm look (seems to come out as a yellow tint in later production screens) of the screen is as easy as switching to the standard srgb profile and then reducing red one or two steps in win 7 calibration. The red accuracy issue is tough to fix and really not a big issue unless you do photo editing, and certainly not a big deal considering it's $50 IPS upgrade.

It has nothing to do with the bad calibration in the stock ICM. The stock ICM is the Flexview ICM, it can be easily removed and replaced with the Windows default RGB ICM, but even switching to the Windows default ICM over the stock Flexview one, results in the exact same ULTRA WARM look. Something is inherently wrong with the actual panels.

There's really only two alternatives to solving this issue, number 1 as you mentioned use the Windows 7 Color Calibrator to compensate and bring down the R/G values which will cool down the panel. Problem with this approach is there is an inherent bug in Windows 7 that makes loading images very very slow when you use the Windows 7 Calibrated ICM. Try it and you'll see, if you create a custom ICM through Win 7's color calibration tool, all images loading through Windows Picture Viewer takes 3-4 times as long. This error has never been fixed, rending the Win 7 Color Calibration useless.

The second option to fix the overtly warm IPS panel is to use a Hardware Calibrator such as Pantone, or a Spyder calibrator. But sadly 99% of society do not own these expensive hardware calibrators, so in the end most people will just have to live with the horrible color production of the X220 panels. Sadly without anything to compare it to, most people will never know how horribly skewed their colors really are. The only I noticed is cause I have several Thinkpads and 2 WQHD panels that are properly calibrated.

The last option of fixing this issue is to use the Intel Color Enhancement Software to bring down the R/G values to comp for the warm tone, but since this option is driven by the Intel GFX drivers, it has to load after Windows is booted, resulting in a odd shift in color everytime you load windows or log off.

Regardless, the IPS panels in the X220 series is not something to be envied. It's the manufacturer of the these panels. The Thinkpad Tablet also uses capacitative touch IPS panels, but shows no signs of these color problems. I have the Tablet, so I know.

This issue is widely talked about many Chinese forums, leading to lots of people on these forums exchanging custom X220 ICM profiles to help people who don't own these hardware calibrator fix their display.