I think those 4CH Sainsmart ones might not be worth it just because the screen must be really small. They say the product dimensions are 4.2" x 2.2". If the bevel is about 1", that means the screen should be about 3.2" x 2.2", that means the diagonal would be about ...
3.2^2 + 2.2^2 = 10.24 + 4.84 = 15.08 sqrt 3.88 or 4"...thats pretty small, its the size of a phone!
I have a Rigol DS1052E that works quite well although the menu can be a bit odd - it is not intuitively obvious how you save a screenshot to a usb flashdrive plugged into the scope (a handy feature but not obvious how to do it). That one is a 50mhz/1GSs/s. The digital storage scopes can work very well, but can be a little quirky on what a signal looks like sometimes (I also have a dual trace Hitachi analog scope). I do find the feature of being able to save a screenshot to a bmp file on a flash drive quite handy though - makes it easy to keep the screenshot for later reference or include it in a word document (or email) for later use. Not sure if all of them have that feature, but I found it nice.
2 channels is just barely enough these days. A "mixed signal" oscilloscope will have 16 or 32 logic inputs as well as 2 or 4 analog inputs. I find this type of scope very useful for Arduino projects. The better ones will even decode the logic to display SPI, I2C or serial data.
Don't discard the PC based USB scopes. They can do a lot more than a standalone scope. You lose some of the flexibility and fault protection of a standalone but I think they're good enough. They are also cheap enough that you can throw it away after a year, after you learn what particular limitation you actually did need. It's a cheap education.
Depends on what you need the oscilloscope for as to what one is most suitable.
If it's for microcontroller/digital type stuff then a normal 2/4 channel oscilloscope is not as useful as a 8/16 channel logic analyser but still worth having for the odd analogue signal.
Another option is something like the Salea Logic 8 (or Logic Pro 8 if the budget allows) as they do both analogue and digital.
No! The Sainsmart DSO203 scopes are junk. The 72MHz claimed bandwidth is a lie based on some marketing person's ignorance of specifications. It is 72Msps (million samples per second) but that is shared between all the channels. The bandwidth is really more like 4MHz. EDN magazine got one and tested it at about 3MHz bandwidth.
All the DSO203 (dee ess oh two zero three) scopes are the same.
They are clumsy to use, have tiny screens, use expensive probes, and can't take much input voltage. They are a potential shock hazard because of the metal case.
I have a Rigol DS1052E, you might find one used cheaper now. 2 channels, 1Gsps shared. I bought the 50MHz version and upgraded the firmware to get 100MHz bandwidth.
They have a newer model that I think I'll be purchasing soon, it is 4 channels. If you go to EEVBlog and look it up, there is an online store that offers a discount to EEVBlog members. Rigol DS1054Z is the 50MHz model for $400 less the discount, and the firmware patch can take it up to 100MHz, also.
Just post on this thread and ask for the discount code. TEquipment ships for free, although you'll have to confirm that for your country.