I would stay clear of paper (eg. Litmus paper) and indicator solutions (eg. Universal Indicator). Paper strips are only a simple "is it more acidic than X" or "is it more alkali than Y". Pigmentation from the soil can also pose a problem. Soil colour and suspension will be the problem with the solutions. A well designed solution such as Universal Indicator might be accurate enough where you need it but it will be difficult to read with soil discoloration. (universal indicator is great for schools as it is easy to use and covers a wide range, unlike litmus paper).
The lab readers are going to be overkill - so cheap digital or analog will be your options. For our Costa Rica work we use a cheap analog reader from a garden center - primarily because it will easily go through aircraft security and customs and cheap if it breaks (also it is more likely to break...)