I started with Arduino UNO, and I was able to perform the following experiments:
1. Android based Smart Phone and Bluetooth Modules HC5
2. Bi-directional radio communication using HC12
3. Parallel LCd and I2C LCD
4. One-wire bus compatible DHT22 type temperature and humidity sensor
5. LM35 analog type temperature sensor
6. DS18B20 type digital 1-Wire Bus compatible sensor
7. SPI Bus compatible SD Card Interfacing
8. MPU6050 3-axis accelerometer and 3-axis gyroscope
9. UART communication with PC using asyn TTL <--->RS232 <---> USB link.
and so many other experiments combining two or more dissimilar sensors together.
There are Arduino MEGA, NANO, DUE and many other varieties; but, the UNO is the most popular one!