Yes, there are several two letter abbreviations, but that’s beside the point. There are significant differences between the two most recent versions of the RPG Maker series, each with it’s own very specific strengths and weaknesses for RPG Game development.
For example, both are nothing more than tile-based game development engines. They offer no specially three dimensional modeling for designing games that would keep up with the modern graphics curve. This isn’t like any casino online in Indonesia that runs on few smooth basic rules and tactics. Instead, RPG Maker has so far focused on a simple world make of 2D sprites and tilesets. Design is much easier as a result, however, and a quality storyline could potentially make up for the graphic shortcomings (compare reading a good book to watching a pointless television show). XP and VX are, however, the first two RPG Maker programs released for sale in America, each for $60.
The first major difference between the two programs is the differences between chipset expansion. VX limits game designers to no more than 5 chipsets, which can hinder the design of a long game with many different maps. With XP, however, game designers can make as many chipsets as necessary for their game.
Also of note is the fact that XP has been available for much longer. Most tutorials and guides teach advanced topics specifically designed for RMXP, making it harder to learn and get started with RMVX. Beginners are often more comfortable with RMVX, as it is designed to have a simpler interface and more of an easy to use design. RPG Maker VX includes some upgrades over XP, which makes game development faster in the beginning, though, which could be advantageous in a number of situations. For example, RMVX has upgrades to the scripting system that XP will never receive, and most program updates will likely be targeted to VX. RMVX also makes adding messages easier with the batch input command.
Many designers agree that VX also has more of a chibi-style look to their games (characters are smaller), which is not currently in style. XP uses larger character sprites, along with everything that goes with them (larger doors, for example), which makes a game seem a little more modern. Moreover, everything in rpgmaker vx has more of a blocky feel. Diagonal walls are nearly impossible (or at least more difficult) thanks to the auto-shadowing, and it’s even difficult to diagonal paths and patches of grass in the newer system. Artistic developers keen on making their own tiles, characters, objects, and resources are more likely to prefer XP’s design.
Overall, the best solution is to download the 30-day trial of each version, and decide which program will work best for your individual needs. Some developers who are not as skilled with programming and chipset design, and would rather focus on creating a fun storyline might be more suited to VX, while others may be more suited to XP. In the end, it’s up to the individual developer’s preferences and needs.