Here is my experience.
Last October(2012) I bought a Cyberpower comp through Newegg. The computer worked fine for the first couple of months. It was January, IIRC, that the unit started to BSOD for no reason. After several trips to the local Computer Repair (Bestbuy-Geeksquad) and the problem was still not fixed. I got with the manufacture and ended up having to replace the Harddrive twice. The second time I had to buy my own copy of Win7Home only to have that HD fail. I asked for a refund/credit towards a new build and still have not heard anything back from them. This was mid August by the time that I sent the last email.
I ended up just building my own computer. Newegg has a great bundle system of giving you compatible parts to choose from. I highly recommend building your own computer. It is a great skill to have. Its like knowing everything about your car and knowing what exactly is wrong (hardware wise) and being able to diagnose it instead of having to take it somewhere to be repaired. My build (estimate) was around $1300. Large case that can be carried, water cooled heat sink, 2TB HD (2x 1tb drives) 5 internal fans + fan controller, decent graphics, decent mom-board, decent optic drive, 16GB RAM. You can make a system that fits your needs better than buying one and customize it from there. I've had no problems with mine so far. It travels ok (its a big computer so its a bit bulky to carry sometimes). I take mine to my friends house about once a month. Before with the Cbyerpower Comp I bough, just moving it from one room to the other caused it to BSOD with no way to start in safemode.
Also, USE WINDOWS 7 PRO SP1 64BIT. Trainz(TS10 and 12) will work just fine with this and is more stable than Win 7 home. This is my opinion too.
These are just my 2 cents. If you want to buy your own and then customize, thats fine. This is just my experince.